Document:

<PAGE>   1
                                                                   Exhibit 10.49

July 26, 2000

                    ADDENDUM NO. 5 TO LEASE AGREEMENT BETWEEN
                  INDUSTRIAL PROPERTIES OF THE SOUTH AS LESSOR
           AND VERILINK CORPORATION (AS SUCCESSOR TO TXPORT, INC.) AS
          LESSEE DATED JUNE, 1993 AND EFFECTIVE SEPTEMBER 22, 1993 AND
                  HEREIN AFTER REFERRED TO AS THE MASTER LEASE

At Lessee's request, this Addendum No. 5 is executed to this date, July 26, 2000
by Lessor and Lessee for the purpose stated within:

A.  Location:     Airport Office Center, 9668 Madison Boulevard, Madison, AL
                  35758
                  First floor office space:  Approximately 10,226 s.f.
                  Third floor office space:  Approximately 19,800 s.f.

B.                Term: Starting December 31, 2000 for a two month period
                  through February 28, 2001.

C.  Rate:         Rent for this time period will remain the same rate,

                  First Floor: $8.98 per s.f. per year x 10,226 s.f. =
                  $91,829.48 (annual) divided by 12 - $7,652.46 (per month).

                  Third Floor: $9.48 per s.f. per year x 19.800 s.f. =
                  $187,704.00 (annual) divided by 12 = $15,642.00 (per month).

All other terms and conditions of the Master Lease remain the same.

VERILINK CORPORATION                        LESSOR

/s/ C. W. Smith                              /s/ Charlene B. Graham
--------------------------------------       -----------------------------------
VP & Corporate Controller

8/10/00                                      8-17-2000
--------------------------------------       -----------------------------------
Date                                         Date

Prepared by:

Industrial Properties of the South
2903 Wall Triana Hwy., Suite 7
Huntsville, AL  35824<PAGE>   1
                                                                   Exhibit 10.50

                                 FIRST AMENDMENT

                              VERILINK CORPORATION
                        1996 EMPLOYEE STOCK PURCHASE PLAN

         VERILINK CORPORATION, a Corporation organized and existing under the
laws of the State of Delaware with its principal place of business in
Huntsville, Alabama, (the "Company'), hereby adopts and publishes on this the
17th day of May, 2000, this Amendment to the 1996 Verilink Corporation Employee
Stock Purchase Plan (the "Plan"), as follows:

         WHEREAS, the Company, effective April 19, 1996, established the Plan
for the benefit of its employees; and

         WHEREAS, said Plan provides that the Company reserves the right for any
reason by action of its Board of Directors to amend in whole or in part any and
all provisions of the Plan; and

         WHEREAS, the definition of "Compensation" as set forth in Section 2(f)
of the Plan is ambiguous; and

         WHEREAS, this Amendment serves to remove any ambiguity from the
definition of "Compensation" as set forth in Section 2(f) of the Plan; and

         WHEREAS, the Plan has, at all times, been administrated in accordance
with the definition of "Compensation" as set forth in this Amendment; and

         WHEREAS, the use of the term "Offering Period" in Section 6(a) is
ambiguous; and

         WHEREAS, the Amendment serves to remove any ambiguity from Section
6(a); and

         WHEREAS, the Plan has at all times been administered in accordance with
Section 6(a) as is set forth in this Amendment; and

         WHEREAS, the Company has also determined that certain other
modifications as to the timing and number of purchases should also be made as
outlined hereinbelow; and

         WHEREAS, by unanimous written consent of the Board of Directors of the
Company, the Board did specifically approve and adopt by resolution the
amendment hereinafter set forth.

         NOW, THEREFORE, in consideration of the premises hereinabove set forth,
the Company amends said Plan, as follows:

<PAGE>   2

                  1. Section 2(f) shall be amended and restated as follows:

         "(f)`Compensation' shall mean an Employee's sales commissions and base
salary from the Company or one or more Designated Subsidiaries, including such
amounts of sales commissions and base salary as are deferred by the Employee (i)
under a qualified cash or deferred arrangement described in Section 401(k) of
the Code, or (ii) to a plan qualified under Section 125 of the Code.
Compensation does not include overtime, bonuses, reimbursements or other expense
allowances, fringe benefits (cash or noncash), moving expenses, deferred
compensation, and contribution (other than contributions described in the first
sentence) made on the Employee's behalf by the Company or one or more Designated
Subsidiaries under any employee benefit or welfare plan now or hereafter
established."

                  2. Section 4(a) shall be amended and restated as follows:

         "(a)The Plan shall be implemented through overlapping or consecutive
Purchase Periods until such time as (i) the maximum number of shares of Stock
available for issuance under the Plan have been purchased or (ii) the Plan shall
have sooner been terminated in accordance with paragraph 19 hereof. The maximum
duration of a Purchase Period shall be twenty-seven months. Commencing on July
1, 2000, the Purchase Period shall be six months, and the Plan shall be
implemented through consecutive Purchase Periods of six months' duration
commencing each January 1 and July 1."

                  3. Section 6(a) shall be amended and restated as follows:

         "(a)At the time a Participant files his/her subscription agreement,
he/she shall elect to have payroll deductions made on each pay day during the
Accrual Period in an amount not exceeding ten percent (10%) of the Compensation
which he/she receives on each pay day during the Accrual Period."

                  4. Section 12(a) shall be amended and restated as follows:

         "(a)The maximum number of shares of the Company's Common Stock which
shall be made available for sale under the Plan shall be 600,000 shares, subject
to adjustment upon changes in capitalization of the Company as provided in
paragraph 18. If on a given Exercise Date the number of shares with respect to
which options are to be exercised exceeds the number of shares then available
under the Plan, the Company shall make a pro rata allocation of the shares
remaining available for purchase in as uniform a manner as shall be practicable
and as it shall determine to be equitable."

<PAGE>   3

         The Company has caused this Amendment to be executed by its duly
authorized officer and its corporate seal to be hereunto affixed on the day and
year first above written.

                                    VERILINK CORPORATION

                                    /s/ Graham G. Pattison
                                    --------------------------------------------
                                    By:  Graham G. Pattison
                                    Its: President

ATTEST:

/s/ C. W. Smith
--------------------------------
By:  C. W. Smith
Its: Secretary

(CORPORATE SEAL)<PAGE>   1
                                                                   Exhibit 10.51

                                 FIRST AMENDMENT

                              VERILINK CORPORATION
                   AMENDED AND RESTATED 1993 STOCK OPTION PLAN

         VERILINK CORPORATION, a corporation organized and existing under the
laws of the State of Delaware with its principal place of business in
Huntsville, Alabama, (the "Company") hereby adopts and publishes on this the
17th day of May, 2000 this Amendment to the Amended and Restated 1993 Stock
Option Plan of Verilink Corporation (the "Plan"), as follows:

         WHEREAS, the Company has determined that an increase in the number of
Verilink Corporation common stock subject to the Plan is necessary; and

         WHEREAS, Section 3(a) of the Plan is hereby amended to increase the
number of Verilink Corporation common stock subject to the Plan; and

         WHEREAS, by written unanimous consent of the Board of Directors of the
Company, said Board did specifically approve and adopt by resolution the
amendment hereinafter set forth.

         NOW, THEREFORE, in consideration of the premises hereinabove set forth,
the Company amends said Plan, as follows:

         1. Section 3(a) shall be amended and restated as follows:

         "(a) An aggregate of not more than 6,800,000 shares of Stock shall be
available for the grant of stock options under the Plan. If an option is
surrendered (except surrender for shares of Stock) or for any other reason
ceases to be exercisable in whole or in part, the shares which were subject to
such option but as to which the option had not been exercised shall continue to
be available under the Plan. Any Stock which is retained by the Company upon
exercise of an option in order to satisfy the exercise price for such option or
any withholding taxes due with respect to such option exercise shall be treated
as issued to the Optionee and will thereafter not be available under the Plan."

         The Company has caused this Amendment to be executed by its duly
authorized officer and its corporate seal to be affixed hereunto on the day and
year first above written.

                                    VERILINK CORPORATION

                                    /s/ Graham G. Pattison
                                    --------------------------------------------
                                    By:  Graham G. Pattison
                                    Its: President

ATTEST:

/s/ C. W. Smith
--------------------------------
By:  C. W. Smith
Its: Secretary

(CORPORATE SEAL)<PAGE>   1
                                                                   Exhibit 10.52

May 3, 2000

Mr. Ron Sibold
3009 Barcody Rd., SE
Huntsville, AL  35802

Dear Ron:

Subject to approval of the Verilink Board of Directors, and upon completion of a
full background and reference check, we will be pleased to extend to you an
offer of employment for the position of Vice President and Chief Financial
Officer.

In this role, your base compensation will be $7,692.31 paid bi-weekly
(annualized salary of $200,000). Executive compensation is reviewed annually
after the end of Verilink's June 30 fiscal year end. Your first salary review
will be following the end of FY 01. Any increase in salary is at my discretion
with approval of the Compensation Committee of the Board of Directors. In this
position you will report directly to me.

         Contingent upon your acceptance of this offer of employment, and
         subject to the Board of Directors' approval, Verilink will grant to you
         a Non-Qualified Stock Option which gives you the right to purchase,
         under terms stated in your Stock Option Agreement, 200,000 shares of
         Verilink Common Stock at the fair market value of that stock as
         determined by the Board of Directors on the first day of your
         employment by Verilink. Vesting occurs over 4 years with 25% of the
         shares vesting upon completion of one full year of employment, and the
         remaining shares vesting at the rate of 2.08% (1/48th) at the end of
         each month thereafter, assuming continuous employment. On or about the
         date of your anniversary each year, Verilink expects to grant you an
         option to purchase an additional 50,000 shares of Verilink Common Stock
         at the then existing fair market value of that Stock, vesting after
         four years of continuous employment after each grant.

You will be provided a sign on bonus of $50,000 (net after taxes) payable within
the first 30 days of employment. If you voluntarily terminate your employment
with Verilink prior to completion of one year's service, you will repay the sign
on bonus in full.

You will receive such benefits as are customarily granted to Verilink employees.
You will receive personal time off (PTO) in accordance with Verilink's existing
policy. PTO initially accrues at the rate of 1-1/2 days per month of employment,
and may be used for vacation, illness, personal business, etc. Verilink confirms
that your health insurance coverage will commence on the first day of your
employment. Please provide the Certificate of Coverage from your current
provider evidencing your existing coverage.

<PAGE>   2

Mr. Ron Sibold
May 3, 2000
Page 2

Attachment 1 sets forth additional benefits currently available to Verilink
Executive Officers. Executive Officer benefits are subject to review from
time-to-time by the Compensation Committee of the Board of Directors. Please
note that Executive Officers do not participate in the profit sharing plan.

You will be eligible to participate in the FY 2001 Executive Incentive Plan at
an on-target bonus of 50%. For FY 2001, 50% of your target bonus is guaranteed
to be paid. Payment will be made following the end of the fiscal year when all
other similar bonuses are paid. Attachment 2 outlines the Plan details.

Your employment with Verilink Corporation is voluntarily entered into and is for
no specific period. As a result, you are free to resign at any time, for any
reason or for no reason. Similarly, Verilink is free to conclude its at-will
employment relationship with you at any time, with or without cause.

In the event of any dispute or claim relating to or arising out of our
employment relationship, you and Verilink agree that all such disputes shall be
fully and finally resolved by binding arbitration conducted by the American
Arbitration Association. HOWEVER, we agree that this arbitration provision shall
not apply to any dispute or claims relating to or arising out of the misuse or
misappropriation of the Company's trade secrets or proprietary or confidential
information.

This offer of employment is subject to a full background check, and is
contingent upon approval of the Board of Directors and receipt of the following:

         A completed employment application.

         Full compliance with the Immigration Reform and Control Act of 1986
         which requires new employees to provide documentation and/or
         identification to establish both identity and work authorization within
         three (3) days of your employment.

         On your date of hire you will be required to sign a Verilink
         Confidentiality Agreement and Change of Control Agreement (Attachments
         3 and 4) as a part of your total employment package.

         If you will be driving your personal automobile for Company business on
         regular basis, you will be required to provide proof of personal auto
         insurance policy.

<PAGE>   3

Mr. Ron Sibold
May 3, 2000
Page 3

If you have any questions regarding the nature of this documentation, please
contact Betsy Mosgrove in the Human Resources Department.

This letter, along with any written proprietary rights agreements that you enter
into with Verilink, set forth the terms of your employment with Verilink and
supersede any prior representations or agreements, whether written or oral. This
letter may not be modified or amended except by an instrument in writing, signed
by Verilink and by you.

Ron, we are pleased to have you join the Verilink team and look forward to your
participation in our continued success.

Sincerely,

/s/ Graham Pattison

Graham Pattison
President and Chief Executive Officer

I accept the foregoing offer:

         /s/ Ronald G. Sibold                                 05/17/00
---------------------------------------                      ----------
NAME                                                             Date

         June 1 - 7, 2000
---------------------------------------
Expected Start Date

GP: meh
Attachments

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