I had purchased a one month 3G 250 mb service on 5/11/10 @ 9:45 am, the end date being 6/10/10.
AT&T send an e-mail message on 6/9/10 stating I had 14 hours remaining until the end of my contract. I replied via my iPad at 7:17 pm on the 9th to cancel.
I received a reply stating that the cancelation was acknowledged shortly thereafter. The next morning I received another e-mail message thanking me for renewing and that my credit card was charged $14.99. I thought that was unfair and was told by a representative of AT&T that I should have canceled 7 days before the end of the contract. Bottom line, be aware.....duffer2