Hmm I may have spoke too soon. I see here http://www.t-mobile.com/shop/addons/...vc_Tab_HotSpot
Thst they have a $14.95 a month charge for tethering and wifi sharing.
I wonder how they would know if I use it anyways? It won't be like it's all the time.
I chatted with a tmobile rep and he said he had no idea how they would know if I was using it without the plan. They need to at least make a popup come up telling you a plan is required when enableing tethering or something. They just added the feature to the phone and no mention of any extra costs. I'll rarely use it so I'm just going to take my chances.