ATT doesn't like 3G's using 2G accounts
This is interesting, ,don't know if it's been reported before but while playing around yesterday I decided to see if the active SIM in my 2G iphone would work in my 3GS. I plugged it in, played for a couple of minutes and then switched back to the real 3GS SIM.
I found this in my mailbox this morning:
Our service records indicate that you are using an iPhone 3G with a data plan designed for other devices.
To avoid unexpected data overage charges and enable Visual Voicemail, please contact your telecom manager, or an AT&T representative at 1-800-331-0500.
Thank you for choosing wireless from AT&T. We appreciate your business.
AT&T Customer Service