This is good news - but I am a bit sceptical here.

What if they do sell the phones (and the N900) over at T-Mobile but at higher prices than most retailers. Then what is the benefit of buying from T-mobile where I actually have to pay more than market prevailing prices just to get a monthly plan ?

If they can price match at leats most retailers and have it on par prices than that makes sence. But if they have already added a premium of 20% on the price and then offer a monthly plan buying plan - that is a bit of a downer for me.