In a nutshell, T-Mobile has long offered a 200 megabyte per month free plan for the iPad. I’ve got an iPad Mini that’s been using this plan from the start and I’ve never paid a penny for it. 200 Meg is not much, but if all you do is email and browsing, good to have. And 200 Meg for free is a pretty solid deal.
Read the article to get a sense of how to get this setup for your cellular iPad.