I am planning on buying a blackberry tomorrow, and have decided to go with T-Mobile, because they seem to be the only carrier in my area that doesn't charge over $70/month for a Blackberry plan. I plan on using the Blackberry for phone and e-mail/texts equally and I really want to be able to develop my own applications for the device. In terms of personal software development, and existing games and entertainment apps, which device should I go for? Looks like my options are the 7100t, 7230, and the 7290.

No one charges over $45.00 for unlimited. Are you certain you shopped correctly?

For unlimited text/e-mail/browsing, and some phone minutes.

With regards to app development, I think the 71xx's and full-qwerty BB's use the same API so there shouldn't be a difference (someone please correct me if I am wrong on this).
As for which form factor is better, I have asked the same question and the resounding response has been: if you do a lot of voice, go 71xx; if you do a lot of email/text, go full qwerty. I have tried both and really prefer the full qwerty models.
Check T-Mo's return policy, you may be able to try both as long as you return within 15 or 30 days (or whatever they tell you...)

Enjoy

I am with Sprint and although they are on CDMA, I have been satisfied with the service. The BB unlimited data plan is only $45, on top of whatever phone plan you choose. Not too bad, although your options for phones now are only the 7250 and 7750....but that will change in a few months with the Nextel merger!

I have Nextel(7520) and I pay like $45 for unlimited BB plan. Now for minutes, I pay $99 for unlimited minutes. So I average about $150, now thats me...I do alot with my phone, you on the otherhand may want a lesser voice plan.