<Page>

                                                                   Exhibit 4.15B





================================================================================


                             SUPPLEMENTAL AGREEMENT

                                      NO. 1

                                       TO

            PURCHASE CONTRACT AGREEMENT DATED AS OF OCTOBER 31, 2001

                                     BETWEEN

                                 MOTOROLA, INC.

                                       AND

                FIRST UNION TRUST COMPANY, NATIONAL ASSOCIATION,
                           AS PURCHASE CONTRACT AGENT


================================================================================


<Page>

         SUPPLEMENTAL AGREEMENT NO. 1 (this "SUPPLEMENTAL AGREEMENT"), dated as
of December 21, 2001, to that certain Purchase Contract Agreement dated as of
October 31, 2001 (the "AGREEMENT"), between Motorola, Inc., a Delaware
corporation (the "COMPANY"), and First Union Trust Company, National
Association, a national banking association, as purchase contract agent (the
"AGENT") for the Holders described in the Agreement.

                                   WITNESSETH:


         WHEREAS, pursuant to the Agreement, the Company issued $1,200,000,000
aggregate stated amount of its Equity Security Units;

         WHEREAS, the Company and the Agent desire to amend the Agreement to
correct a definition in the Agreement that is currently inconsistent with
another definition in the Agreement;

         WHEREAS, Section 8.1(e) of the Agreement provides a manner by which the
Agreement may be amended by the Company and the Agent, without the consent of
any Holders, in order to, among other things, correct or supplement any
provisions in the Agreement inconsistent with any other provisions, provided
such action does not adversely affect the interests of the Holders; and

         WHEREAS, pursuant to and in accordance with Section 8.1(e) of the
Agreement the Company and the Agent have determined that this Supplemental
Agreement does not adversely affect the interests of the Holders and the Company
and the Agent have agreed to enter into this Supplemental Agreement;

         NOW, THEREFORE, in consideration of the mutual agreements contained
herein and for other good and valuable consideration, the receipt and adequacy
of which are hereby acknowledged, the parties hereto agree as follows:

         Section 1. AMENDMENT.

         1.1 AMENDMENT. Pursuant to Section 8.1(e) of the Agreement, Section 1.1
of the Agreement is hereby amended by deleting the definition of "Redemption
Amount" in its entirety and replacing it with the following:

             "Redemption Amount" means, in the case of a Tax Event Redemption
             occurring prior to a successful remarketing of the Notes, for each
             Note, the product of (i) the principal amount of such Note and (ii)
             a fraction whose numerator is the applicable Treasury Portfolio
             Purchase Price and whose denominator is the aggregate principal
             amount of Notes outstanding on the Tax Event Redemption Date, and
             in the case of a Tax Event Redemption


<Page>

             occurring after a successful remarketing of the Notes, for each
             Note, the par value of the Notes.

         Section 2. MISCELLANEOUS.

         2.1. GOVERNING LAW. THIS SUPPLEMENTAL AGREEMENT SHALL BE GOVERNED BY
AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT
REGARD TO ITS PRINCIPLES OF CONFLICTS OF LAWS.

         2.2. CONFIRMATION OF THE AGREEMENT. Except as amended hereby, the
Agreement shall remain in full force and effect and is hereby ratified and
confirmed in all respects.

         2.3. MULTIPLE COUNTERPARTS. The parties may sign multiple counterparts
of this Supplemental Agreement. Each signed counterpart shall be deemed an
original, but all of them together represent one and the same agreement.

         2.4. SEPARABILITY. Each provision of this Supplemental Agreement shall
be considered separable and if for any reason any provision which is not
essential to the effectuation of the basic purpose of this Supplemental
Agreement shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

         2.5. HEADINGS. The captions of the various section headings of this
Supplemental Agreement have been inserted for convenience of reference only, are
not to be considered a part hereof, and shall in no way modify or restrict any
of the terms or provisions hereof.

         2.6. THE AGENT. The Agent shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Agreement or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Company.

         2.7. DEFINITIONS. All terms defined in the Agreement shall have the
same meaning in this Supplemental Agreement unless otherwise defined herein.

                            [signature page follows]

<Page>

         IN WITNESS WHEREOF, the parties hereto caused this Supplemental
Agreement to be duly executed as of the day and year first above written.


                                         MOTOROLA, INC.


                                         By: /s/ Carl F. Koenemann
                                             ------------------------------
                                             Name:  Carl F. Koenemann
                                             Title: Executive Vice President
                                                    and Chief Financial Officer


                                         FIRST UNION TRUST COMPANY, NATIONAL
                                         ASSOCIATION, as Purchase Contract Agent


                                         By: /s/ Edward L. Truitt, Jr.
                                             -------------------------------
                                             Name:  Edward L. Truitt, Jr.
                                             Title: Vice President