T-Mobile does prepaid data, but the rates are so exorbitant that I'm not even tempted.
I do have a "Smart" phone, but it's hobbled by not having cellular data access. I have to find a free wifi connection if I want to get on the Interwebz.
This is annoying at times, since the phone's navigation feature is heavily dependent on having a data connection. Obviously it has to be connected to the Internet to find restaurants and download satellite imagery, but there's more going on than that: it seems to take a REALLY long time to find its own position if it doesn't have a network connection.
This means my phone doesn't have a real GPS chipset - rather, some sort of ersatz GPS that needs a cellular data hookup to work properly. Maybe most smartphones are this way, I don't know.
It's annoying enough that I'm considering buying a standalone GPS unit, just for navigation. It would pay for itself quickly vs. a few months of having a cellular data plan.