I am locked in a contract with t-mobile but want to get ether the 920 or the 808.
If I get an unlocked 920 will it work with my sim card? I don't care about data I just need it to call/text, and possibly use wifi every now and then.
Do I need the data plan to use GPS/turn by turn?
Not sure about the 808 but for the 920, yes. The only way to get the 920 to work with T-Mobile (as of now that is) is with either an UNLOCKED ROGERS Lumia 920 or with one of the Developer's Build Units given away at the Developer Conference. The Dev Units (Developer Units) will cost you a pretty penny though and can be found on ebay. For a Rogers Unlocked, do a search on the forums. There's info on how you can go about getting one. I'm on USA T-Mobile and love my 920!