Yes this phone works with T mobile contract..

Yes this phone will work with a T-Mobile contract.

Yup. Just take it to a Teen Mobile location and they'll do it for you, free of charge!

Yes you can use your own card and the is no cost after purchase

I bought this for my daughter it came with a new card her old one would not fit. But we took it to the T-Mobile store and had them put in her # and activate it, and they did it for no charge.

I purchased mine at best buy but it came with the card they helped me to install it but instructions come inside package easy to follow, sim card has to match, sim cards are slightly smaller or larger in some phones.
I wasn't charged extra but some places will sell phone and charge extra for SIM card.

I have a contract from tmobile and when i lost my phone i ended up buying this one to use in the mean time before i qualified to upgrade. I just had to buy the mini sim card but since you have one it should work.

Yes you can uses it for prepaid from T-Mobile or another service provider like ultra mobile(ultra.me) which has much cheaper unlimited plans.

Yes on both Wifi and GPS counts.

I use the wifi capability at home. Pretty reliable.

The GPS is somewhat solid. Not the best. Then again, the inherent flaws could be in the Nokia mapping app.

Yes, the Nokia Lumia 251 can connect with wifi and has GPS capability.