cell phone

Does anyone use one of these on their phone? I see quite a few people use them. Just wondering if you like it? https://www.popsockets.com/

Does anyone know anything about T-mobile or have them? I see they have come into our area now, I have always heard decent things about them. Basically for what we are paying for now we could get on T-mobile but get unlimited internet for the same cost, plus free Netflix etc...