I have a code 628 or g28 on a cordless att 3658b phone what do I do

SOURCE: How to de-register handset from

First deregister all handsets:

Step 1: At the base, press MENU, scroll to BASE SETTINGS, then press OK.

Step 2: Using the base dialpad, enter * * 3 3 5 7 8 2

Step 3: Re-register each system handset:

At the base, press MENU, scroll to DISPLAY BASE-ID, then press OK. The 15-digit base ID number will be displayed.

Step 4: Using the handset dialpad, enter the base ID number. Repeat the registration procedure for each system handset. Each handset is assigned a number in the order of registration