@bandofbrothers:
Eh, it probably won't be that much of one. I -do- have a N770(which I upgraded with an 8GB SDHC, I might add), and IIRC maemo 5 is internally like Os2006/7(I.e. Debian based), so I shouldn't have much trouble tweaking it etc.
The phone side of things will be interesting, but so long as there is a simple way to dial a number and press "call", no worries there.

@geneven:
So long as I can get one of those Tmobile sims and it will -work- with my N900, I'm sure I won't have any trouble. And, from the responses, it looks like it will without issue.

I just bought a new Tmobile sim off ebay(Cause I'm -sure- it will be faster than off Nokia's own site, and a tad cheaper at $5.75). Only little glitch is that it doesn't come with an activation code. I did some googling however, and it seems all I will have to do is call Tmobile customer support and get them to give me a code... if I read things right.

If any of you see hurdles in my plan, please let me know.

-Rob