Two years ago, when I bought an origianal iPhone, and then returned it, the customer service experience with AT&T was pretty horrid (see iPhone Lansing).
This time, I had received an initial bill in the mail for $122.07, covering the $36 activation fee, initial few days of service plus a month in advance at the $40 voice + $30 data rate (no text messages), and the usual ridiculous array of surcharges, add-ons, and taxes. When I returned the iPhone 3GS on July 6th, they told me to call AT&T service in a day or two to get a final figure reflecting the cancellation of service.
When I got around to calling on July 13, I expected to pay for activation, 18 days of service, etc, or about $80. The agent looked up my record and asked why I had cancelled (bad network service, inadequate coverage area) and then "took care of" the bill. He apologized that it took so long, but when I asked what my balance was, he said zero! I'm expecting to receive a paper bill confirming that in a few days. But what a nice surprise. My trial with the iPhone only cost $19.90 -- the Apple 10% restocking fee.
The "new" AT&T comes out looking pretty good, even though they have an overloaded, and limited area, network. And Apple looks like a douche-bag with their 10% restocking fee, even though they have a pretty nice device.