The message never came through for me either. If you just send the text that AIM forwarding says to use to "sign on" then it will just work. It has been for me. Let me see if I can find the doc I used to figure out the text you have to send in order to sign onto aim using your phone.
*EDIT* found it. Here is the PDF. On page 3 (according to Adobe, not the page nurabers) it details how to sign on. In a nutshell you need to send a text message to 265000 and the message should just be YourScreenName{space}YourPassword
Then you can scroll down to page 11 to find out how to send IMs and junk. Have fun!
