A year ago when I got the 3GS I thought I'd be clever and sign up for the absolute cheapest plan they had. "I'll just be judicious and save my rollover minutes!" said I, unaware that my gums tend to flap profusely when talking on the phone.
"I'll use 3rd-party texting and Skype minutes and it'll be no sweat," I thought to myself as I played with the newfangled compass on my phone. Sadly, this plan was dashed when I started the travel season. Between Macworld, SXSW and WWDC I wound up with hundreds of minutes and texts in overages. My bills were over $200 each month. The dude did not abide by this plan.
Today at the Apple Store the AT&T reps on duty claimed I couldn't change my rates, and hastily handed me a sheet that had something to do with my SIM card. So the Apple rep took me to activate my phone, and there I was able to upgrade my text and bring in my grandfathered unlimited data plan, but couldn't adjust the calling minutes.
On the way to my brother's house I called the AT&T customer service number (that's 611 on your iPhone) and within 15 minutes they not only upgraded me to unlimited going forward, but they adjusted my previous overages into a less painful range. Kudos to AT&T! They even allowed us to upgrade ahead of the normal schedule, which I greatly appreciate.
* Coverage is getting better. I noticed a marked improvement in San Francisco over just this past January.
** AT&T dropped the ball in 2009, but learned from that mistake and picked up the ball in 2010. As I said, things are improving.