Hello, I am a Customer Care rep for AT&T and I would like to say that I really do understand how this was aggravating for you from the very beginning, and I apoligize that you had so much difficulty upgrading your equipment. Honestly, you should have went to an AT&T Company Owned Retail store from the beginning. Best buy is a “National Retailer” and they do not have as much training or access to your account as the internal sales channels do. It is possible the the Best Buy reps either 1. Did not know what to do. Or, 2. did not even have access to the information they needed to figure out what was wrong.
This issue that you experienced was due to network and billing system conversion that has been going on for years. In the billing system, it requires all “Blue” customers to convert to the “Orange” network before they can do an equipment upgrade. We call this the “Migration Process.” AT&T has put blocks in the billing system that requires customers to eventually Migrate to the Orange network. This entails getting a new SIM card, a compatible phone and often changing rate plans also, since the “blue” rate plans are normally very old and are sales expired.
This is a very rare issue that impacts customer’s that have been with us for many many years and still have fairly old equipment. It is not a common issue, which may be why you had so much difficulty, and once again I apologize, on a lighter note I hope your enjoying your new phone!
As always, thank you for choosing AT&T, we really appreciate your business and have a pleasant day… 🙂
Dear anonymous AT&T rep:
Yes, as  a matter of fact, I am enjoying my new phone very much.
By the way, that phone is a HTC EVO 4G, on the Sprint network. I’ve terminated my service with AT&T after six years.
Have a nice day.