That's not correct. On the Even More plans, the phones are subsidized and you can pay for them on a 20-month plan. On the the Even More Plus plans the phones are not subsidized and you can also get the 20-month payment option. And it's the same selection of phones on both types of plans. [Edit: Looks like CaptainGinyu beat me to the punch. Hope my explanation is also useful.]

That aside, it seems like it would have to be T-Mobile for the N900, given the 1700 3G band. There have been a lot of rumors about T-Mobile releasing the N900 already. Of course, to get the subsidy, you'd have to sign up for a two year contract on an Even More plan, which is $20 more per month for the plans with data. So over the two years you'd pay $480 more in the monthly cost of your plan, plus the presumably $199 up front for the device. That means You'd pay a total of $679 extra, which is $100 more expensive that just buying the N900 outright from Amazon and even more expensive than the worst price you can get buying directly from Nokia ($649). This is the great lie of phone subsidies, they're a bad deal for the consumer and the carriers make money on them in the long run.