You forgot to say what country you from....

With regards to the 3g coverage, here in the UK 3g is better then 2g, but this may not be the same in other countries.

with regards to the other 2 question is yes.

I have t-mobile in the UK and I got something called a free internet booster with my new contract, meaning i get free internet on my n900 for 24 months, based on fair usage policy, but from experience t-mobile in the UK only caps you if you go over, unlike what other networks which have hidden charges if you go over the fair usage. I highly recommend t-mobile to everyone, top service, top business module. My monthly contract is only £20 per month including 300 free minutes and free text messages(can't recall how many).