Im not sure how exactly T-Mobile's service is, I have a 7290 threw Cingular and use there blackberry email service..
ect.. and It alows you to add email accounts to it like
,hotmail,yahoo configure outlook,domino ect.... and when you get a message in that account it shows up on the BB and you can reply just like normal and what not..
and from what I understand and have read you can create an account if you already havent on T-Mobiles site ( https://my.t-mobile.com/Login/
) and create a BB email account there and add up to 10 email addys. or as they put it "All you need is the e-mail address, username, and password for each of your existing e-mail accounts. Once you log in to My T-Mobile, you can set up BlackBerry Internet E-mail, add or delete e-mail accounts, configure your settings, add filters ect" ..
not sure if that will help or not, im sure some of the BB Geniuses on here can come up with other very good solution aswell.