I think that the T-Mobile unlimited Data plan is still available. It may not be easily found on their Website. I think one needs to call T-Mobile and ask them to specifically add it to one's account. I used this Data Plan as recently as December 2008 when I started messing around with my Nokia 770 after quite a few months.

Also there is a limited $ 9.99 plan that will give you 50 MB of (data downloads ) web surfing along with so many Text messages etc. This Plan is similar to the Unlimited Data plan but is simply limited to the 50 MB total download. If one is happy to look at ones e-mail once or twice a day instead of totally involved Web surfing, then this would be a good option to use.