Interesting question, keep in mind as far as i know TMO's unlimited plan is just email, not all data. Maybe someone with tmo could provide details.

You could probably open a business account, with a tax id # http://www.irs.gov/businesses/small/...102767,00.html

which you can get online

Also keep in mind, at least with at&t you'll need to keep a voice plan on your account to buy the $65 int'l data plan. So it will really cost $105 + taxes and fees probably bring it to $115-120