[Galaxy S III General] BarryH_GEG:
I'm guessing at some of this stuff just like you guys. Here's where I think people are getting tripped up.

1) Moving from a high-end phone and plan to a low-end phone and plan.

Ordering a new iPhone, SGS3, One XL to sell on eBay and then calling in two weeks later to downgrade to a flip phone with a dumb phone data plan is a red flag unto itself. You can give the AT&T agent any reason you want but if they are suspicious they'll flag your account for audit. A human looks at the type of phone you're (supposed to be) using, type of call and data activity you're consuming, changes in patterns over a couple of months of usage, etc. So if your IMEI is missing or tied to a dumb phone and you're consuming as much data as you did historically the human will interrupt your data plan and comment your account for a CSR to move you to the right plan when you call in. This could also explain the "I see you're using a i9300" as some people have reported.

2) Micro-SIM

Asking AT&T for a micro-SIM when you're on a non-smartphone data plan is a red flag unto itself. They have four devices with micro-SIMs: 1) iPhone, iPad, One X, and SGS3. None belong on a non-smartphone plan. Again, if a smart agent/rep flags your account you'll end up audited. You're far better off cutting your own SIM than trying to get a new one and raising attention.

3) Use Premier if you can.

AT&T Premier is everywhere. If you have a relative, friend, or acquaintance that works somewhere with Premier you can piggy-back off their access. Each Premier account has a designated rep whose e-mail is usually on the intranet page. Going through my Premier rep has me with:

1) Two devices (UK G-Tab 10.1 and One X) on non-smartphone data plans with no IMEI recorded on my account and SIMs that accurately reflect my data plan.

2) A new micro-SIM configured for the data for non-smartphones plan provisioned on my account that was overnighted to me for free.

3) No questions asked as to what I'm doing or why and a lot of what I’m sharing as to the inner workings of AT&T are from discussions he and I have had.

A Premier rep is probably your best bet for getting changes made to your existing account and a micro-SIM while still flying under the radar. If you can find someone who can share their Premier access you can link your existing non-Premier account online before reaching out to the Premier rep. In fact, you'd have to. From there you can communicate via e-mail.

Even without Premier, starting new service is a lot easier than changing an existing plan. Getting a contract-less dumb phone calling plan with data should be as simple as a phone call with a standard SIM overnighted to you. If they ask for an IMEI tell them you'll call it in when you're ready to activate your service. You can then activate online and have no IMEI associated with your account. I think using gobs of data each month when the IMEI of the phone shown in your account (pulled from an old dumb phone) doesn’t logically support it is probably one of the audit triggers.

For those changing plans in-store or over the phone, it's a crap shoot and you have no recourse if you're caught. You're literally asking AT&T to give up revenue they've already been receiving from you to do something their T&C specifically forbids. Do you feel lucky? ;)