T-mobile. iPad is just wifi since the network connection comes from the phone.
I wanted to get an Air first as it is a real computer. However, I actually had to have something by July 17, they're on the verge of releasing a new Air, and the new one is likely to have enough improvements that I won't be happy about paying too much for the old one. If you're wondering why I had to get a new machine, I need to be seen working on something other than what I really use (i.e. very old, but perfectly serviceable cheapo machines)
But for travel purposes, the iPad looks like it might do the trick. Minimalist, does most of the things I need on the road (document composition/editing, VPN access, server management, simple presentations, web browsing) and the other stuff can wait. Also, it's a better entertainment device than the Air which is more fun when you're on the road all day.