<PAGE>

                                                                   EXHIBIT 10.31

                      [CONFIDENTIAL TREATMENT REQUESTED]
 
                              PURCHASE AGREEMENT

                     ULTRADATA'S CALIFORNIA SERVICE BUREAU

ULTRADATA Corporation, a Delaware corporation ("ULTRADATA") and Premier Systems,
Incorporated, an Iowa corporation ("PSI") hereby enter into this agreement for
the transfer of ULTRADATA's service bureau located at 5000 Franklin Drive,
Pleasanton, CA 94588 (the "California Bureau"):

1. "CU CONTRACTS" means all of ULTRADATA's rights under its data processing
   contracts with the credit unions listed below (the "Contracted CUs").
   ULTRADATA hereby assigns to PSI, and PSI hereby assumes, all of its rights in
   and obligations under the CU Contracts, effective as of September 30,
   1997(the "Closing Date").  If ULTRADATA does not have the right to
   unilaterally assign a CU Contract, then the sale of that contract is subject
   to ULTRADATA's ability to obtain that credit union's consent to this
   assignment.  PSI agrees to use its best efforts to assist ULTRADATA in
   obtaining from each Contracted CU a novation of its respective CU Contract
   eliminating ULTRADATA as a party thereto as soon as practicable following the
   Closing Date.
 
2. PURCHASE PRICE.  PSI will buy, and ULTRADATA will sell, Hardware and CU
   Contracts as detailed in sections 1 and 4, and ULTRADATA will license the
   Software as detailed in section 3, for a purchase price of $1,100,000 as
   adjusted pursuant to section 1 and subsection 2.C.  Hardware and Software
   that is licensed or assigned to PSI as applicable under this Agreement is
   listed on Schedules A-1 through A-4, attached hereto and incorporated by this
   Agreement.  PSI will pay the purchase price in cash as follows:

     A.  A $250,000 down payment payable upon execution of this Agreement.
 
     B.  Four quarterly payments of $125,000 each payable on December 31, 1997,
         March 31, 1998, June 30, 1998, and September 30, 1998.
 
     C.  Four quarterly "Hold Back" payments of $87,500 each payable during the
         second year of this Agreement on December 31, 1998, March 31, 1999,
         June 30, 1999, and September 30, 1999. Quarterly Hold Back payments
         described herein are contingent upon the Contracted CU remaining on the
         PSI bureau through out the calendar quarters ended on the above dates;
         provided however, the second year Hold Back payments assigned to each
         Contracted CU, as listed on Schedule B, will be paid to ULTRADATA
         within 30 days of the Contracted CU signing a PSI contract of three
         years or greater. The balance of the remaining Quarterly Hold Back
         payments will be reduced by the acceleration of payments to ULTRADATA
         by PSI, if a PSI Agreement with a Contracted CU is signed prior to the
         end of the scheduled payment.

______________
* Confidential treatment has been requested with respect to certain portions of
  this exhibit. Confidential portions have been omitted from the public filing
  and filed separately with the Securities and Exchange Commission.

                                       1
<PAGE>
 
     D.  If a Contracted CU converts off the PSI bureau any time prior to
         signing a contract with PSI or September 30, 1999, whichever is
         earlier, the Quarterly Hold Back payments will be reduced on a pro-rata
         basis as defined on Schedule B.

3. "SOFTWARE" when capitalized means all of the software currently used by
   ULTRADATA in the operation of the California Bureau for the benefit of the
   Contracted CUs, including operating programs, data base programs, modules,
   custom programs, interfaces, and related programs, whether developed by
   ULTRADATA or by one or more third parties. Schedules A-1 through A-4 as
   applicable, detail Software licensed and or assigned under this Agreement.
 
     A.  ULTRADATA STANDARD PROGRAMS. To the extent the Software is comprised of
         programs developed by ULTRADATA of a type that ULTRADATA is currently
         licensing to PSI pursuant to the Software Agreement, these programs
         (including AIX/UNIX, UniData, Uniplex, ALPS, and FSP), such Software
         will be deemed to be licensed under the Software Agreement, and PSI's
         rights in the Software will be determined pursuant to the Software
         Agreement. For purposes of this Agreement, "Software Agreement" means
         that certain Software and Services Agreement between ULTRADATA and PSI
         effective as of July 1, 1997.
         
     B.  ULTRADATA CUSTOM PROGRAMS. ULTRADATA grants PSI a nonexclusive license,
         pursuant to the terms and conditions of the Software Agreement, to use
         all Software which is comprised of programs developed by ULTRADATA
         which are not of a type that ULTRADATA is currently licensing to PSI
         pursuant to the Software Agreement. This includes custom programs and
         related third party interfaces, such as online ATM interfaces and
         shared branching interfaces. PSI will have the right under this license
         to use this Software on any system operated by PSI within the scope of
         the licenses granted under the Software Agreement. ULTRADATA will
         provide PSI with a copy of the source code for this Software upon
         request to enable PSI to support and maintain this Software.

     C.  OTHER PROGRAMS.  ULTRADATA will assign to PSI all of its rights in the
         license's of Software which is comprised of programs developed by
         someone other than ULTRADATA and used solely by the California Bureau,
         subject to the terms and conditions of the agreement under which
         ULTRADATA obtained such Software.

4.  "HARDWARE" means the equipment listed on Schedules A-1 through A-4 as
    applicable, whether located at the California Bureau or at a Contracted CU.
    To the extent the Hardware is leased to Contracted CUs, ULTRADATA hereby
    assigns to PSI, and PSI hereby assumes, all of ULTRADATA's rights in and
    obligations under 

                                       2
<PAGE>
 
   these leases, and ULTRADATA's sale of the leased items is subject to the
   rights of the Contracted CUs pursuant to these leases. Schedule A includes a
   list of all such leases. ULTRADATA warrants that it has good title to the
   Hardware, free and clear of all liens and encumbrances other than the leases
   to the Contracted CUs of equipment located at these credit unions and any
   rights or encumbrances imposed by the original lessor of any Hardware not
   owned by ULTRADATA. ULTRADATA warrants that the Hardware is in good operating
   condition, and that the IBM R40 CPU located at the California Bureau is under
   a maintenance contract with IBM. ULTRADATA assigns to PSI all of ULTRADATA's
   rights in the manufacturer's warranties for the Hardware. PSI will coordinate
   moving the Hardware from ULTRADATA to PSI and will assume the costs of
   packaging, shipping and other related costs. PSI agrees to use its best
   efforts to assist ULTRADATA in obtaining from each Contracted CU a novation
   of any Hardware lease eliminating ULTRADATA as a party thereto as soon as
   practicable following the Closing Date.
 
5.  TRANSITION PROVISIONS.

      A.   HOLD HARMLESS. PSI is not assuming any of ULTRADATA's contracts with
           third party vendors, including maintenance contracts and contracts
           for data lines, other than lease agreements with respect to the
           Hardware as specified in section 4 above. Subject to the terms and
           conditions hereof, ULTRADATA agrees to hold PSI harmless from any
           claims under these vendor contracts and from any claims by a
           Contracted CU for services performed or which should have been
           performed by ULTRADATA pursuant to a CU Contract prior to the Closing
           Date. PSI agrees to hold ULTRADATA harmless from any claims by a
           Contracted CU for services performed or which should have been
           performed, and for any other claim or liability arising out of the CU
           Contracts, Hardware, assigned Hardware leases or activities of PSI as
           contemplated under this Agreement, on or after the Closing Date. The
           party granting a hold harmless will also hold the other party
           harmless from the costs of defending against such a claim, including
           reasonable attorneys' fees; provided that as a condition to the
           obligations of the party responsible for holding harmless (the
           "Indemnifying Party") under this subsection 5.A, the other party (the
           "Indemnified Party") will (a) promptly notify the Indemnifying Party
           of any such claim; (b) tender full control of the defense and
           settlement of such claim to the Indemnifying Party, provided that the
           Indemnified Party will have the right to reasonably approve the
           counsel selected by the Indemnifying Party and to participate at its
           own expenses in such defense and settlement, and provided further
           that the Indemnifying Party will not settle any such claim in a
           manner materially adverse to the Indemnified Party without the
           Indemnified Party's written consent, which will not be unreasonably
           withheld or delayed; and (c) provide such assistance as the
           Indemnifying Party may reasonably request.

                                       3
<PAGE>
 
      B.   OPERATIONAL SUPPORT. ULTRADATA will provide operational support to
           the California Bureau consistent with the operational support
           provided by ULTRADATA prior to the Closing Date until April 30, 1998
           or until an earlier date specified by PSI with at least 30 days
           advanced written notice. This operational support will include full
           staffing of the California Bureau in accordance with current levels
           of personnel including the weekend work necessary to convert
           Contracted CUs to PSI's facility, first level CRC to the California
           Bureau, disaster recovery and back up support for the California
           Bureau. PSI will pay ULTRADATA **** per month for this operational
           support. Payment will be made on the last business day for each month
           by wire transfer, under this operational contract. During this period
           of operational support, ULTRADATA will provide PSI with remote access
           to the computer system at the California Bureau under specifications
           established by PSI and mutually agreed upon by both parties.
 
      C.   CONVERSION SUPPORT. ULTRADATA will assist PSI in the planning and
           conversion of Contracted CUs from the California Bureau to PSI's West
           Des Moines facility. ULTRADATA will provide reasonable levels of
           training to PSI personnel on the custom modules and interfaces used
           at the California Bureau, and ULTRADATA will provide support in
           accordance with the support provided under the Software Agreement for
           these modules and interfaces for a reasonable time after the
           conversion to PSI's West Des Moines facility as mutually agreed upon
           by both parties.
 
      D.   LICENSE FEES. **** PSI will use best efforts to obtain signed
           processing agreements with each Contracted CU as soon as practicable
           following the Closing Date. Within 24 months after the Closing Date
           and provided a Contracted CU has signed a processing agreement with
           PSI, PSI will pay ULTRADATA **** of the software license and
           maintenance fees specified in the Software Agreement or other
           applicable agreement. During this 24 month period, the members of the
           Contracted CU's will be treated as members in excess of **** members
           for purposes of applying the license and maintenance fees under
           section 6.2 of the Software and Services Agreement. After the end of
           this 24 month period, PSI will pay the full amount of the software
           license and maintenance fees specified in the Software Agreement or
           other applicable agreement; provided however, at all times following
           the Closing Date, PSI will pay to ULTRADATA the full cost of software
           license and maintenance fees applicable to new software licensed for
           use by a Contracted CU. PSI shall obtain ULTRADATA's prior written

______________
* This information has been omitted as the Company is seeking confidential 
  treatment for such information.
                                       4
<PAGE>
 
           approval of any processing agreement between PSI and a Contracted CU,
           which has a term of less than 36 months.
           
      E.   NON-COMPETE. ULTRADATA will not convert a Contracted CU to an in-
           house system utilizing the ULTRAFIS software for a period of ****
           following the Closing Date. ULTRADATA will not Participate in
           the Business of operating a service bureau to service any of the
           Contracted CUs utilizing ULTRAFIS software for a period of ****
           after the Closing Date. "Participate in the Business" means to
           operate or invest in such a service bureau, or to license the use of
           ULTRAFIS software to an unrelated service bureau if ULTRADATA has
           received written notice at the time of licensing that the service
           bureau intends to service any of the Contracted CUs.

6.   LIMITATION OF WARRANTIES. Except as set forth in this agreement, ULTRADATA
     will provide the Software and the Hardware "AS IS" WITH NO WARRANTY
     WHATSOEVER, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED
     WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
     WARRANTIES ARISING FROM A COURSE OF DEALING OR TRADE PRACTICE.
     
7.   LIMITATIONS OF LIABILITY. The Software Agreement is unaffected by this new
     Agreement. With the exception of the Software Agreement, the commitments
     explicitly stated in this Agreement will be the only obligations of the
     parties with respect to the subject matter of this Agreement. NEITHER PARTY
     WILL BE LIABLE TO THE OTHER PARTY FOR ANY CONSEQUENTIAL, INCIDENTAL, OR
     EXEMPLARY DAMAGES ARISING OUT OF OR IN CONNECTION WITH THIS AGREEMENT,
     whether based on breach of contract, tort, negligence, product liability,
     or otherwise, or whether the party has been advised of the possibility of
     such damage.
     
8.   GENERAL PROVISIONS.
 
      A.   ASSIGNMENT. Neither party may assign this Agreement without the prior
           written consent of the other party.
           
      B.   INTERPRETATION OF THIS AGREEMENT. With the exception of the Software
           Agreement, this Agreement constitutes the entire contract between the
           parties as of the Closing Date. With respect to the Software
           Agreement, the provisions of section 5.D of this Agreement will
           control over the provisions of the Software Agreement to the extent
           specified in Section 5.D.. This Agreement revokes and replaces all
           other prior written or oral contracts between the parties covering
           the same subject matter with respect to performance after the Closing
           Date. This Agreement can only be modified by a written letter or
           other document signed by both parties. The use of the term
           "including" followed by 







* This information has been omitted as the Company is seeking confidential 
  treatment for such information.
                                       5
<PAGE>
 
           examples means that the examples are illustrative of the general
           concept, but the examples are not intended to be an exhaustive
           recitation of the general concept. If any provision of this Agreement
           is found invalid or unenforceable, that provision will be enforced to
           the maximum extent permissible, and other provisions of this
           agreement will remain in force.

      C.   VENUE AND GOVERNING LAW. If PSI deems it appropriate to initiate
           litigation, such litigation will be commenced in California and be
           pursuant to California law. If ULTRADATA deems it appropriate to
           initiate litigation, such litigation will be commenced in Iowa and be
           pursuant to Iowa law.
 
      D.   FORCE MAJEURE. Neither party will be responsible for any failure to
           perform due to causes beyond its reasonable control, including but
           not limited to, acts of God, war, riot, civil or military
           authorities, fire, flood, earthquake, accident, or labor dispute.
 
      E.   INDEPENDENT CONTRACTOR. The parties are independent contractors.
           There is no relationship of partnership, joint venture, franchise, or
           agency between the parties.

      F.   NOTICES. A party will give formal notices required by this agreement
           to the other party's chief executive officer at the other party's
           principal office. Formal notices will be given by either first class
           mail or overnight courier service.

ULTRADATA CORPORATION                          PREMIER SYSTEMS, INCORPORATED
 
By:        /s/ Philip D. Ranger                By:     /s/ Thomas Griffiths
 
Name:     Philip D. Ranger                     Name:   Thomas Griffiths
 
Title:    Vice President and CFO               Title:  Chairman
 
Date:     September 30, 1997                   Date:   September 30, 1997
 

                                       6
<PAGE>
 
                              Purchase Agreement
                                 Schedule A-1

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------------------------------
                                              SERVICE BUREAU EQUIPMENT INVENTORY
-----------------------------------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------------------------------
ITEM # SERIAL #  DESCRIPTION              MAKE                   MODEL            QUANTITY        USE
<S>    <C>       <C>                      <C>                    <C>              <C>             <C>
-----------------------------------------------------------------------------------------------------------------------------------
   1             CPU                      HP                     H70                     1        Host CPU
   2             CPU                      HP                     E45                     1        Optical Server
   3             CPU                      REST                                           2        Remote Banking Servers
   4             CPU                      Intervoice             IBM PS/2 77s            1        VRIII PC
   5             Terminal/Keyboard        HP                     700/96                  2        Host & Optical Console
   6             Terminal/Keyboard        Optiquest              1000S                   2        Remote Banking Console & Terminal
   7             Terminal/Keyboard        IBM                    14L8                    1        VRIII Console
   8             UPS                      Emerson                AccuTower               1        Host System UPS
   9             UPS                      Emerson                AccuPower Gold          2        Comm Equip UPS
  10             UPS                      A{C                    SmartUPS 1400           1        Remote Banking UPS
  11             SureStore Optical        HP                     330fx                   1        Optical Disk Storage
  12             Printer                  Okidata                MicroLine 184 Turbo     1        Host Monitor Printer
  13             Terminal/Keyboard        Wyse                   Wyse50                  1        Host Terminal
  14                                      REST                   SupraExpress 33.6       1        Remote Banking
  15             Annex                    Xylogics               Annex3                  3
  16             Synchronous Engine       Telamon                N/A                    12        Bisynch 0
  17                                                                                              Bisynch 1
  18                                                                                              Bisynch 2
  19                                                                                              Bisynch 3 (LBS)
  20                                                                                              ESP Live ATMs
  21                                                                                              PAR ATMs
  22                                                                                              SIL Shared Branch
  23                                                                                              SSS ATMs
  24                                                                                              BVF ATMs
  25                                                                                              OAK ATMs
  26                                                                                              SIL Live ATMs
  27             Modem                    AJ                     1445                    2        Security Modems
  28             Modem                    Codex                  3512                    1        JEF Shared Branch
  29             Modem                    Codex                  2660                    1        (Not connected)
  30             Modem                    Codex                  3380                    1        PARISHIONERS
  31             Modem                    Codex                  3261                    2        Bisynch Transmissions
  32             Modem                    Codex                  3260                    2        Bisynch Transmissions
  33             Modem                    Codex                  2205                    1        Bisynch Transmissions
  34             Modem                    Racal-Milgo            OmniMode 96             1        SIL ATM's (owned by EDS)
  35             Modem                    Practical Peripherals  PM144MT2                2        ALPS Credit Report
  36             Modem                    Practical Peripherals  PM288MT II V.34         1        ALPS Credit Report
  37             DSU                      Codex                  3500                    4        JEF
  38                                                                                              OAK
  39                                                                                              SIL3
  40                                                                                              SIL2
  41             DSU                      ADTRAN                 DSU SW56 DBU            3        CAL
  42                                                                                              SIL Main(1)
  43                                                                                              SIL Main(2)
  44             DSU                      Motorola UDS           SW 56 11                1        Dial Backup (owned by Deluxe)
  45             DSU                      Motorola               3520                    1        Owned by Deluxe
  46             ISU Terminal Adaptor     ADTRAN                 ISU 2X64                1        ISDN restoral for CU's
  47             Router                   3COM                   Netbuilder II           1        Frame Relay
  48             T1DSU                    ADTRAN                 TSU                     2        MCI Frame Relay
  49                                                                                              GST Frame Relay
  50             Power Sensor             Sensaphone             1000                    1
  51             Hub                      Gateway                G/EtherTwist            1        LAN Connection
  52             Open Network Server      TyLink                 ONS150                  1
-----------------------------------------------------------------------------------------------------------------------------------
</TABLE>

                                       7
<PAGE>
 
                              Purchase Agreement
                                 Schedule A-2
                        Service Bureau IBM Information

<TABLE> 
<CAPTION> 
------------------------------------------------------------------------------------------------------------------------
IBM System
<S>                 <C>      <C>        <C>           <C>            <C>        <C>              <C>
------------------------------------------------------------------------------------------------------------------------
                   
------------------
Unix Licenses     
------------------
UniData Licenses  
------------------
Uniplex Licenses  
------------------
Uniplex Release   
------------------
Ultrafis Release  
------------------
ALPS Release      
------------------
ALPS Licenses     
------------------
VR Level (2,3,4)  
------------------
VR @ UD?          
------------------
ATM Online/Offline
------------------
ATM Vendor        
------------------
Shared Branch y/n 
------------------
SB Vendor         
------------------
Optical MR y/n    
------------------                                                  * * * * 
UA Release        
------------------
Debit/Visa Vendor 
                  
------------------
VISA Level (1,4)  
------------------
ACH/Deposit       
Network Vendor    
------------------
Share Draft       
Processor         
------------------
System            
Hardware:         
------------------
Model             
------------------
Memory            
------------------
Disk              
------------------
Tape Drives       
------------------
</TABLE> 

<TABLE> 
<CAPTION> 
IBM System          SIL              FAM              BV               CSC              SSS              CVA      
<S>                 <C>              <C>              <C>              <C>              <C>              <C>           
Unix Licenses                                                                                                     
------------------
UniData Licenses  
------------------
Uniplex Licenses  
------------------
Uniplex Release   
------------------
Ultrafis Release  
------------------
ALPS Release      
------------------
ALPS Licenses     
------------------
VR Level (2,3,4)  
------------------
VR @ UD?          
------------------
ATM Online/       
Offline           
------------------
ATM Vendor        
------------------
Shared Branch                                                     * * * * 
y/n               
------------------
SB Vendor         
------------------
Optical MR y/n    
------------------
UA Release        
------------------
Debit/Visa        
Vendor            
------------------
VISA Level (1,4)  
------------------
ACH/Deposit       
Network Vendor    
------------------
Share Draft       
Processor         
------------------
System            
Hardware:         
------------------
Model             
------------------
Memory            
------------------
Disk              
------------------
Tape Drives       
------------------
</TABLE> 

______________
* This information has been omitted as the Company is seeking confidential 
  treatment for such information.

                                       8
<PAGE>
 
                              Purchase Agreement
                                 Schedule A-3


-------------------------------------------------------------------------------
                    Service Bureau Credit Unions Using ALPS
-------------------------------------------------------------------------------


                  CREDIT UNION               NUMBER OF MEMBERS


                                                  * * * *


                                            ------------------
                  Total                           * * * *

______________
* This information has been omitted as the Company is seeking confidential 
  treatment for such information.


                                       9

<PAGE>
 
                              Purchase Agreement
                                 Schedule A-4


-------------------------------------------------------------------------------
                Third Party Interfaces on the Service Bureau
-------------------------------------------------------------------------------


             Interface For:       Interface With (vendor):
             Share Drafts         WesCorp
                                  Bank of the West
                                  First National Bank
                                  Travelers
                                  Federal Reserve Bank
                                  Colorado CU League

             ------------------------------------------------
             ACH & Deposit        Federal Reserve Bank
             Network              EIS
                                  WesCorp

             ------------------------------------------------
             Debit/Visa           EIS
                                  Equifax/First Security

             ------------------------------------------------
             ATM                  Deluxe on-line
                                  FiServ off-line
                                  Deluxe off-line
                                  Trans Alliance off-line
                                  EDS on-line
                                  EDS off-line

             ------------------------------------------------
             Shared Branch        Deluxe

             ------------------------------------------------

                                       10
<PAGE>
 
                                 SCHEDULE B

                   Contracted CU's and Holdback Allocation
<TABLE> 
<CAPTION> 

--------------------------------------------------------------------------------
                                           Second Year                Monthly
"Contracted CU"                             Hold Back                Hold Back 
                                            Allocation               Allocation
--------------------------------------------------------------------------------
<S>                                        <C>                       <C> 
 Total Hold Back Allocation                 $350,000                  $29,167
================================================================================
</TABLE> 

______________
* This information has been omitted as the Company is seeking confidential 
  treatment for such information.


                                       11