Figured I'd be nice and point out that technically for today only Tmobile had a deal where any smartphone was free for new users and those available for an upgrade. However, their systems were down for most of the day, so they extended the sale and it's still running tomorrow.
Getting my free Samsung Galaxy s2 tomorrow! (b'')b
On a note, they cost money, but you get a full mail-in rebate. So for the s2 you have to pay $250, and then get a $250 mail-in rebate. If you are poor and can't front the money, then it won't be worth it.