Document:

<PAGE>
                                                                  Exhibit 10.1.5

                                  BAKER CENTER
                               AMENDMENT OF LEASE

DATE:       May 15, 1997

BETWEEN:    ST. PAUL PROPERTIES, INC.
            435 Peavey Building
            730 Second Avenue South
            Minneapolis, MN 55402                 ("Landlord")

AND:        ONE CALL TELECOM, INC.
            1200 Baker Building
            706 Second Avenue South
            Minneapolis, MN. 55402                ("Tenant")

IN RESPECT OF PREMISES IN:         Baker Building, Minneapolis, MN

LANDLORD AND TENANT hereby agree as follows:

1.    In this Amendment of Lease:

      (a)   "Building" means Baker Building located in the city of Minneapolis,
            Minnesota.

      (b)   "Premises" means 3,555 square feet of space on the 12th floor of the
            Baker Building, as set out in the Lease.

      (c)   "Lease" means the lease between Landlord and Tenant dated July 29,
            1996, covering the Premises.

      (d)   "Amendment Date" means May 15, 1997.

2.    Effective on the Amendment Date, Article 3.01 of the Lease is deleted, and
      the following is substituted therefor:

      3.01  Term  Notwithstanding Article 3.02 and 3.03, the Term of this Lease
            shall be five (5) years, eleven 11 months and ten (10) days
            beginning on the twenty second day of the month of July 1996 and
            ending on the last day of the month of June 2002, unless terminated
            earlier as provided in this lease.

                                       1
<PAGE>

3.    Effective on the Amendment Date, Article 4.01 of the Lease is deleted and
      the following is substituted therefor:

      4.01  Tenant shall pay to Landlord as Annual Rent for the Premises the
            annual sum of thirty-one thousand nine hundred ninety-five and
            00/100 dollars ($31,95.00) in respect of the period July 22, 1996
            through June 30, 1997, and thirty-seven thousand three hundred
            twenty-seven and 50/100 dollars ($37,327.50) in respect of the
            period July 1, 1997 through June 30, 2002, payable in advance and
            without notice in monthly installments (each equal to one-twelfth of
            the Annual Rent) on the Commencement Date and on the first day of
            each month thereafter during the Term.

4.    Effective on the Amendment Date, the following is added as Article 27.00:

      ARTICLE 27.00 Additional Premises

      27.01 Additional Premises means the area on the twelfth floor of the
            Building as indicated on Exhibit 1 attached hereto, hereby deemed to
            contain 1,776 square feet plus, for the calculation of Rent only, an
            additional 266 square feet of unallocated space in the Building.

      27.02 Term  The Term on the Additional Premises shall commence on the
            "Additional Premises Commencement Date" which shall be July 1, 1997,
            subject to the substantial completion of Tenant Improvements set
            forth in Article 28.00 of this Amendment of Lease and terminate on
            the same day of the Premises.

      27.03 Rent  Tenant shall pay to Landlord as Annual Rent for the Additional
            Premises, the annual sum twenty-one thousand four hundred forty-one
            and 00/100 dollars ($21,441.00). Rent shall be paid in equal monthly
            payments at the time and in the same manner as Annual Rent payments
            are to be made pursuant to the Lease.

      27.04 Occupancy Costs  Tenant shall pay, as additional rent, Occupancy
            Costs in respect of the Additional Premises at the time and in the
            same manner as payment of Occupancy Costs are to be made pursuant to
            the Lease.

                                       2
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5.    Effective on the Amendment Date, the following is added as Article 28.00:

      ARTICLE 28.00 Landlord's Work

      28.01 Landlord will construct Tenant Improvements to the Additional
            Premises in accordance with the "Plan" which is attached hereto as
            Exhibit 2. All other work necessary for occupancy of the Additional
            Premises by Tenant will be Tenant's responsibility.

6.    Effective on the Amendment Date, the following is added as Article 29.00:

      ARTICLE 29.00 Option Space

      29.01 Option Space  In the event there has been no default by Tenant,
            Tenant shall have the right to lease the space ("Option Space")
            containing 1,461 square feet, more or less, on the twelfth (12)
            floor of the Building as generally indicated on Exhibit 1, plus for
            calculation of Rent only, an additional 219 square feet of
            unallocated space in the Building, upon the terms and conditions set
            out in this Article 29.00, if

            (a)   Tenant is not in default under this Lease at the time such
                  option is exercised and at the time such option is to
                  commence, and

            (b)   Tenant delivers to Landlord not later than October 1, 1997
                  written notice exercising its right to lease the Option Space.

            If Tenant fails to exercise its right to lease the Option Space,
            Tenant shall have no further right to lease the Offer Space under
            this Article 29.00.

            Terms A lease of space under this Article 29.00 shall contain the
            following:

            (a)   Annual Rent shall be equal to $17,640.00 payable in monthly
                  installments in accordance with the Lease;

            (b)   Occupancy Costs shall be determined in accordance with this
                  Lease;

                                       3
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            (c)   Commencement Date for the lease of Option Space shall be the
                  later of August 1, 1998 or Fifteen (15) days notice from
                  Landlord that the Offer Space is available.

            (d)   Term shall end on the expiration or earlier termination of the
                  Lease, subject to the same option to extend as the Lease;

            (e)   Landlord will deliver the Option Space to Tenant with the
                  following work done at Landlord's expense:

                  o     Demolition and construction of interior walls in
                        accordance with attached Exhibit 3.

                  o     Install new building standard carpet and wall covering
                        throughout the Option Space. Carpet and wall covering
                        are to be selected by Tenant from Landlord building
                        standard selection.

                  o     Patch where needed due to demolition of interior walls.

                  o     Patch, as close as reasonably possible to existing,
                        ceiling in areas where interior walls were removed.

                  o     Relocate existing door as shown on attached Exhibit 3.

                  o     Install one (1) light fixture as shown on attached
                        Exhibit 3.

            (f)   These other terms and conditions shall be as set out in this
                  lease.

      29.02 Documentation  Within fifteen (15) days of receipt from Landlord,
            Tenant shall execute and deliver to Landlord those instruments
            Landlord may request to evidence any lease of space under this
            Article 9.00.

                                       4
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      29.03 Non-Severabililty  The rights of Tenant under this Article 29.00
            shall not be severed from this Lease or separately sold, assigned,
            or otherwise transferred, and shall expire on the expiration or
            earlier termination of this Lease.

7.    The following is added as Article 30.00

      ARTICLE 30.00 EXTENSION OF TERM

      30.01 Grant  In the event there has been no default by Tenant, Landlord
            hereby grants to Tenant the one-time option to extend the Term upon
            the terms and conditions set out in this Article 30.00, if

            (a)   Tenant is not in default under this Lease at the time such
                  option is exercised and at the time such extension is to
                  commence; and

            (b)   Tenant delivers to Landlord, not later than nine (9) months
                  prior to the end of the original Term, written notice
                  exercising its option to extend the Term.

      30.02 Terms  During the extended Term:

            (a)   Annual Rent shall be equal to Market Rent as of the
                  commencement of that extended Term, but in no event less than
                  the highest amount set out in Article 4.01;

            (b)   Occupancy Costs shall be as determined in the manner set out
                  in Landlord's then-current standard form of lease for the
                  Building;

            (c)   the Term shall be three (3) years, commencing upon expiration
                  of the original Term; and

            (d)   the other terms and conditions shall be as set out in this
                  Lease, except that there shall be no further right of renewal
                  (in the case of a one time option).

                                       5
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8.    The following is added as Article 31.00:

      ARTICLE 31.00 MARKET RENT

      31.01 Definition  "Market Rent" means the amount of cash (exclusively of
            Occupancy Costs) which a landlord would receive annually by then
            renting the space in question assuming the Landlord to be a prudent
            person willing to lease but being under no compulsion to do so,
            assuming the Tenant to be a prudent person willing to lease but
            being under no compulsion to do so, assuming a lease term equal to
            the term in question, and assuming lease containing the same terms
            and provisions as those contained in this Lease.

      31.02 Determination of Market Rent  Whenever Annual Rent under this Lease
            is based on the Market Rent Landlord shall initially determine the
            Market Rent and shall thereupon give Tenant notice of the amount of
            Annual Rent and the basis on which Landlord made its determination
            of that amount. Upon receipt of that notice, Tenant shall pay the
            Annual Rent stated in that notice in the manner set out in Article
            4.01.

      31.03 Disagreement on Market Rent

            (a)   If Tenant does not agree with the Landlord's determination of
                  Market Rent, Tenant shall nevertheless pay to Landlord the
                  amount set out in the notice Landlord gives under Article
                  31.02 and Tenant shall give notice to Landlord of that
                  disagreement within ten (10) days of receipt of that notice
                  from Landlord.

            (b)   If Tenant gives Landlord notice of disagreement, Landlord
                  shall immediately refer the matter to an individual (the
                  "Expert") selected by Landlord, subject to approval by Tenant,
                  such approval not to be unreasonably withheld, who shall be
                  deemed to be acting as an expert and not as an arbitrator. The
                  Expert shall make a determination of Market Rent as
                  expeditiously as possible.

            (c)   If the Market Rent as determined by the Expert is greater than
                  the Tenant has paid in accordance with the notice given under
                  Article 31.02, Tenant shall immediately pay to Landlord the
                  difference and shall after that make the

                                       6
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                  payments of Annual Rent as determined by the Expert. If the
                  Market Rate as determined by the Expert is less than Tenant
                  has paid in accordance with the notice given under Article
                  31.02, Landlord shall immediately pay to Tenant the difference
                  and Tenant shall after that make the payments of Annual Rent
                  as determined by the Expert.

            (d)   If the Market Rent as determined by the Expert is less than
                  95% of the amount set out in the notice under Article 31.02,
                  Landlord shall bear the costs and reasonable expenses of the
                  Expert. If the Market Rent as determined by the Expert is 95%
                  or more of the amount set out in the notice under Article
                  31.02, Tenant shall bear the costs and reasonable expenses of
                  the Expert.

Except as specifically provided herein, the terms and conditions of the Lease
are confirmed and continued in full force and effect

This Amendment of Lease shall be binding on the heirs, administrators,
successors and assigns (as the case may be) of the parties hereto.

IN WITNESS OF THIS LEASE Landlord and Tenant have properly executed it as of the
date set out on page one.

LANDLORD:                                    TENANT:

ST. PAUL PROPERTIES, INC.                    ONE CALL TELECOM, INC.

By: /s/ R. William Inserra                   By: /s/ Ronald W. Mullins
    --------------------------------             -------------------------------
    R. William Inserra
    Vice President Asset Management          Its: President

5-27-97                                      Ronald W. Mullins
------------------------------------         -----------------------------------
Date Executed                                Please Type Signature

                                             19 MAY 97
                                             -----------------------------------
                                             Date Executed

                                             -----------------------------------
                                             Witness to the signature of Tenant
                                             if not incorporated.

                                       7
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                                                                       Exhibit 1

                                    [GRAPHIC OMITTED]

<PAGE>

                                    [GRAPHIC OMITTED]

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                                                                       Exhibit 3

                                    [GRAPHIC OMITTED]<PAGE>
                                                                  Exhibit 10.1.6

                                  BAKER CENTER
                     SECOND LEASE OF ADDITIONAL OFFICE SPACE

DATE:       August 4, 1997

BETWEEN:    ST. PAUL PROPERTIES, INC.
            410 Peavey Building
            730 Second Avenue South
            Minneapolis, MN 55402                      ("Landlord")

AND:        Advanced Telecommunications, Inc.
            730 Second Avenue South
            Suite 410
            Minneapolis, Minnesota 55402               ("Tenant")

IN RESPECT OF PREMISES IN: Peavey Building, Minneapolis, Minnesota

LANDLORD AND TENANT hereby agree as follows:

1.    In this Second Lease of Additional Space:

      (a)   "Building" means Peavey Building located in the city of Minneapolis

      (b)   "Prime Lease" means the lease between Landlord and Tenant dated
            August 14, 1996 as amended by the First Amendment of lease dated
            September 5, 1996, covering 3,737 square feet in the Building.

      (c)   "Term" means that period of time commencing August 15, 1997 and
            terminating upon thirty (30) day notice from either party.

      (d)   "Additional Space" means 1,522 square feet of space on the Fourth
            floor of the Building, as shown crosshatched on Exhibit 1 hereof.

      (e)   "Rent" means $1,200.00 during each month of the Term.

      (f)   All other words and phrases, unless otherwise defined herein, have
            the meanings attributed to them in the Prime Lease.

                                       1
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2.    Landlord hereby demises and leases the Additional Space to Tenant, and
      Tenant accepts the lease of the Additional Space to have and to hold
      during the Term, on the same terms and conditions as are contained in the
      Prime Lease except as herein otherwise provided, and expressly excepting
      the following:

      (a)   Rent - Tenant shall pay the Rent to Landlord in advance in equal
            monthly payments at the times and in the manner as rental payments
            are to be made pursuant to the Prime Lease.

      (c)   Condition of Additional Space - Tenant shall be deemed to have
            examined and accepted the Additional Space in the condition as of
            the date hereof, and no tenant or other allowance shall be paid by
            Landlord to Tenant in respect of the Additional Space.

      (d)   Inapplicable Clauses - The following clauses of the Prime Lease
            Article 4.02, 4.06 and 6.02 shall not be applicable to this Lease.

      (e)   Default - Any default by Tenant under the Prime Lease shall be
            deemed to be a default hereunder, and any default hereunder shall be
            deemed to be a default under the Prime Lease.

      (f)   Termination - If the Prime Lease terminates for any reason
            whatsoever, this Lease shall terminate on the same date.

      (g)   Occupancy Costs - Tenant shall pay as additional rent Occupancy
            Costs in respect of the Additional Space at the times and in the
            manner as payments of Occupancy Costs are to be made pursuant to the
            Prime Lease.

                                       2
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Except as specifically provided herein, the terms and conditions of the Prime
Lease are confirmed and continued in full force and effect.

This Lease shall be binding on the heirs, administrators, successors and assigns
(as the case may be) of the parties hereto.

IN WITNESS OF THIS LEASE Landlord and Tenant have properly executed it as of the
date set out on page one.

LANDLORD:                                    TENANT:

ST. PAUL PROPERTIES, INC.

By:                                          By: /s/ Michael A. Donahue
    --------------------------------             -------------------------------
    R. William Inserra
    Vice President Asset Management          Its: Treasurer

                                             Michael A. Donahue
------------------------------------         -----------------------------------
Date Executed                                Please Type Signature

                                             8/8/97
                                             -----------------------------------
                                             Date Executed

                                             -----------------------------------
                                             Witness to the signature of Tenant
                                             if not incorporated.

                                       3
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                                                                       Exhibit 1

                                [GRAPHIC OMITTED]

<PAGE>

                                                               September 3, 1997

TO:         Advanced Telecommunications, Inc.

FROM:       ST. PAUL PROPERTIES, INC.
            Madison Marquette Realty Services
            The Managing Agent

RE:         Leasing Space In Baker Center

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

Delivery Date:          October 1, 1997.

Premises:               Approximately 9528 rentable square feet (approximately
                        8507 usable square feet) of office space on the twelfth
                        floor of the Peavey Building, as shown on the attached
                        plan.

Term:                   Five (5) years commencing October 1,1997 and expiring
                        September 30, 2002.

Annual Net Rent:        The annual net rate per rentable square foot for each
                        lease year will be as follows:

                                   Year         Net Rate
                                   ----         --------
                                     1          $10.00
                                     2          $10.00
                                     3          $11.50
                                     4          $13.00
                                     5          $13.00

Occupancy Costs:        In addition to the Annual Net Rent, tenant will pay a
                        proportionate share of the building's operating costs
                        and real estate taxes "Occupancy Costs." Such
                        proportionate share of Occupancy Costs will be paid
                        monthly on an estimated basis and adjusted at the end of
                        each calendar year. The 1997 estimate of Occupancy Costs
                        is $8.69 per rentable square foot, plus electricity
                        consumed by tenant in its own space.

<PAGE>

Tenant Improvements:    Landlord will buildout the Premises in accordance with a
                        mutually approved plan using building standard
                        materials. Landlord will contribute up to $8.00 per
                        square foot leased ("Landlord Contribution") to offset
                        the cost of tenant improvements to the Premises. All
                        costs incurred by Landlord in excess of Landlord's
                        Contribution will be paid by tenant upon invoice from
                        Landlord.

                        Use Of Premises: The Premises shall be used and occupied
                        only for general office use.

                        Tenant Inducements: Tenant's current lease for 4261
                        rentable square feet which expires September 30, 2001
                        would be terminated and a new lease would be prepared on
                        this proposal.

Qualification Of
Proposal:               This proposal assumes no outside brokerage commissions
                        will be paid by landlord for the leasing of this space.

Building Management:    Madison Marquette Realty Services ("Madison Marquette")
                        was formed in 1995 by the merger of Madison Realty
                        Partnership and Marquette Partners. Madison Realty
                        Partnership was a Cincinnati based real estate group
                        involved in acquisition and redevelopment of commercial
                        properties. Marquette Partners was a Minneapolis
                        based real estate company providing a full
                        range of real estate services including asset
                        management, property management, leasing & marketing to
                        owners and investors of real estate.

                        Today, Madison Marquette is a nationally recognized real
                        estate company involved in virtually every aspect of
                        commercial real estate. Madison Marquette's current
                        property portfolio consists of 11,370,151 square feet in
                        retail and office properties in 12 states. The
                        composition of the portfolio is 37% regional shopping
                        centers, 25% community centers, 21% office and
                        industrial.

Building Ownership:     St. Paul Properties, Inc. is a wholly owned subsidiary
                        of the St. Paul Fire and Marine Insurance Company which
                        is the principal operating subsidiary of The St. Paul
                        Companies, Inc. The St. Paul Companies commemorated
                        their 140th anniversary in 1993. St. Paul Properties,
                        Inc. was established in 1981 to acquire real estate
                        investments on behalf of St. Paul Fire and Marine
                        Insurance Company.

<PAGE>

                        The mission of St. Paul Properties is to diversify the
                        general investment portfolio of St. Paul Fire and Marine
                        by investing in real estate and to achieve a longer term
                        total rate of return which is competitive with that
                        provided by other investments. As of December 31, 1995,
                        St. Paul Properties had invested $700 million in 20
                        different projects across the United States in such
                        major cities as Minneapolis, New York, Washington D.C.,
                        Atlanta, Chicago, Denver, Los Angeles, and San
                        Francisco.

Offer Expiration:       The business terms as offered in this proposal will
                        expire thirty (30) days from the date of this proposal.

Not Binding:            This proposal is not contractual in nature. Neither
                        party shall be bound to the other unless and until a
                        formal written agreement of lease (or amendment of
                        lease) in form and substance satisfactory to all parties
                        is concluded.

<PAGE>

                                      Memo

To:       Mike Donahue

From:     Chuck Howard

RE:       Lease Proposal

                            Brochure of proposal note

Current Premises           3737  RSF
Additional Premises         528  RSF
                           ----
Total SF                   4265  RSF

Net Rata

            9/15/96  -     9/30/97           $6.00
            10/1/97  -     9/30/98           $7.00
            10/1/98  -     9/30/99           $9.00
            10/1/99  -     9/30/01           $12.00

Any net over term    =     $9.20/RSF

Net Rent Recapture

      $9.20 (avg Face Rate) - of 6.00 (Actual Face Rate) =
      $3.20/of for previous 9/15/96 through 9/30/97 =
      $3.20x4265 =                                                    $13,648.00
                                                                      ----------

      Unamortized Tenant Improvements @ 10%, 60.5 months =
      $705.32/month x 48 months (surrendered term) =                  $33,855.00
                                                                      ----------

      Landlords Recapture of unpaid cost though Rent =                $47,503.30

$47,503 amort @ 10%, 60 months = $12,011.58/yr

$12,011.58 / 9528 = $1.26/of/yr

STANDARD NET   Rates Being Achieved in the P.U. Building Area

$9.00 for 70 months        9.00 + 1 = 10
12.00 for 30 months        12.00 + 1 = 13

<PAGE>

                [LETTERHEAD OF MADISON MARQUETTE REALTY SERVICES]

March 7, 1997

Mr. Mike Donahue
Advanced Telecommunications, Inc.
410 Peavey Building
730 Second Avenue South
Minneapolis, MN 55402

RE: Lease of Additional Office Space

Dear Mike:

Enclosed is one (1) fully-executed copy of the Lease of Additional Office Space
between Advanced

Telecommunications, Inc. and St. Paul Properties, Inc.

If you have any questions, please call.

Thank you.

Sincerely,

MADISON MARQUETTE REALTY SERVICES, L.P.
As Managing Agent for St. Paul Properties, Inc.

/s/ Charles F. Howard

Charles F. Howard
Vice President
Office and Industrial Properties Division

Enc.:  lease of additional office space (1)

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