I got this from a friend----
Just got this text from att.
AT&T Free Msg: You're a valued AT&T customer. We'd like to add 1000 bonus Rollover minutes to the mobile number ending in xxxx. There's no cost or obligation to you. It's our way of saying thank you. To have your minutes added, reply "YES" by 9/7/2011. Reply stop to end mktg msgs.
Doesn't hurt to try.
Text Yes to 11113020
Then I got.
Thank you for responding to our free 1000 bonus Rollover Minute offer. You will receive a confirmation message upon validation of this mobile account.
They said that friends of theirs that had unlimited plans still got this to work for them.