SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
Schedule 13G
Under the Securities Exchange Act of 1934
(Amendment No. 3)*
ADTRAN, INC.
 (Name of Issuer)

Common Stock
 (Title of Class of Securities)

00738A106
 (CUSIP Number)
Check the following box if a fee is being paid with this statement ____. (A fee is not required only if the filing person: (1) has a previous statement on file reporting beneficial ownership of more than five percent of the class of securities described in Item 1; and (2) has filed no amendment subsequent thereto reporting beneficial ownership of five percent or less of such class.) (See Rule 13d-7.)
*The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.
The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).
(Continued on following page(s))

Page 1 of 5 Pages

CUSIP NO. 00738A106             13G             Page 2 of 5 Pages

1  Name of Reporting Person
   S.S. or I.R.S. Identification No. of Above Person

   T. ROWE PRICE ASSOCIATES, INC.
   52-0556948

2  Check the Appropriate Box if a Member of a Group*

                                                       (a) ____
   NOT APPLICABLE                                     (b) ____

3  SEC Use Only

   ______________________________

4  Citizenship or Place of Organization

   MARYLAND

Number of      5  Sole Voting Power
               **
Shares            1,094,600

Beneficially   6  Shared Voting Power
               **
Owned By Each     -0-

Reporting      7  Sole Dispositive Power
               **
Person            4,918,073

With           8  Shared Dispositive Power

                  -0-

9  Aggregate Amount Beneficially Owned by Each Reporting Person

   4,918,073

10 Check Box if the Aggregate Amount in Row (9) Excludes Certain
   Shares*

   NOT APPLICABLE

11 Percent of Class Represented by Amount in Row 9

   6.9%

12 Type of Reporting Person*

   IA

               *SEE INSTRUCTION BEFORE FILLING OUT!
         **Any shares reported in Items 5 and 6 are also
                       reported in Item 7.
SCHEDULE 13G
PAGE  3  OF   5

Item 1(a) Name of Issuer:
          Reference is made to page 1 of this Schedule 13G

Item 1(b) Address of Issuer's Principal Executive Offices:

          901 Explorer Blvd., Huntsville, Alabama 35086

Item 2(a) Name of Person(s) Filing:

          (1)  T. Rowe Price Associates, Inc. ("Price
               Associates")

          (2)  _______________________________________

_____     Attached as Exhibit A is a copy of an agreement between
          the Persons Filing (as specified hereinabove) that this
          Schedule 13G is being filed on behalf of each of them.

Item 2(b) Address of Principal Business Office:

          100 E. Pratt Street, Baltimore, Maryland 21202

Item 2(c) Citizenship or Place of Organization:

          (1) Maryland

          (2)  ________

Item 2(d) Title of Class of Securities:

          Reference is made to page 1 of this Schedule 13G

Item 2(e) CUSIP Number: 00738A106

Item 3    The person filing this Schedule 13G is an:

  X       Investment Adviser registered under Section 203 of the
          Investment Advisers Act of 1940

_____     Investment Company registered under Section 8 of the
          Investment Company Act of 1940

Item 4    Reference is made to Items 5-11 on page 2 of this
Schedule 13G.
SCHEDULE 13G
PAGE   4   OF   5

Item 5 Ownership of Five Percent or Less of a Class.

  X    Not Applicable.

_____  This statement is being filed to report the fact that, as
       of the date of this report, the reporting person(s) has
       (have) ceased to be the beneficial owner of more than five
       percent of the class of securities.

Item 6 Ownership of More than Five Percent on Behalf of Another
       Person

       (1) Price Associates does not serve as custodian of the
           assets of any of its clients; accordingly, in each
           instance only the client or the client's custodian or
           trustee bank has the right to receive dividends paid
           with respect to, and proceeds from the sale of, such
           securities.

           The ultimate power to direct the receipt of dividends
           paid with respect to, and the proceeds from the sale
           of, such securities, is vested in the individual and
           institutional clients which Price Associates serves as
           investment adviser.  Any and all discretionary
           authority which has been delegated to Price Associates
           may be revoked in whole or in part at any time.

           Except as may be indicated if this is a joint filing
           with one of the registered investment companies
           sponsored by Price Associates which it also serves as
           investment adviser ("T. Rowe Price Funds"), not more
           than 5% of the class of such securities is owned by
           any one client subject to the investment advice of
           Price Associates.

       (2) With respect to securities owned by any one of the T.
           Rowe Price Funds, only State Street Bank and Trust
           Company, as custodian for each of such Funds, has the
           right to receive dividends paid with respect to, and
           proceeds from the sale of, such securities.  No other
           person is known to have such right, except that the
           shareholders of each such Fund participate
           proportionately in any dividends and distributions so
           paid.

Item 7 Identification and Classification of the Subsidiary Which
       Acquired the Security Being Reported on By the Parent
       Holding Company.

       Not Applicable.

Item 8 Identification and Classification of Members of the Group.

       Not Applicable.
SCHEDULE 13G
PAGE   5   OF   5

Item 9   Notice of Dissolution of Group.

         Not Applicable.

Item 10  Certification.

         By signing below I (we) certify that, to the best of my
         (our) knowledge and belief, the securities referred to
         above were acquired in the ordinary course of business
         and were not acquired for the purpose of and do not have
         the effect of changing or influencing the control of the
         issuer of such securities and were not acquired in
         connection with or as a participant in any transaction
         having such purpose or effect.  T. Rowe Price
         Associates, Inc. hereby declares and affirms that the
         filing of Schedule 13G shall not be construed as an
         admission that Price Associates is the beneficial owner
         of the securities referred to, which beneficial
         ownership is expressly denied.

                            Signature.

         After reasonable inquiry and to the best of my (our)
         knowledge and belief, I (we) certify that the
         information set forth in this statement is true,
         complete and correct.

         Dated: February 14, 2007

         T. ROWE PRICE ASSOCIATES, INC.

         By:  /s/ Henry H. Hopkins
              Henry H. Hopkins, Vice President

         Note: This Schedule 13G, including all exhibits, must be
filed with the Securities and Exchange Commission, and a copy
hereof must be sent to the issuer by registered or certified mail
not later than February 14th following the calendar year covered
by the statement or within the time specified in Rule 13d-1(b)(2),
if applicable.

12/31/2006