Jailbreak, then purchase 3G Unrestrictor. It's really great for being able to stream video over 3G using Joost. Not that I'd know from personal experience or anything.
Depending upon how much video you want to watch, and how much you want to listen to Slacker I'd bet you could go over 5GB in a month. You might even be able to just by streaming Slacker at work for 8 hours per day, 5 days per week.
And we haven't even started talking about tethering. Of course I wouldn't know anything about that either.
Just an iPhone user here trying to make the most out of the $30 paid to AT&T for 5GB of data transfer each month... --
It's simple: Obama is lying about health care. His plans require rationing, and openly fund abortions and euthanization. And his continued association with ACORN only shows that he supports its illegal and immoral activities. Remove Obama from office now.