I recently canceled my AT&T contract, paid my ETF, bought a straighttalk SIM, and now $50/mo ($45 plus taxes.) for 'unlimited' service. It works without unlocking because straighttalk is an AT&T based MVNO (or at least the sim I bought from them is.). It's not perfect, but I'll make back my ETF in four months.
You might be on the AT&T cell network, but you're being proxied onto StraightTalk's gateway to get out onto the Internet. And that's the part which sucks. :)
