My family bought unlimited data a few weeks ago and it worked fine until I switched phones. I broke my phone so I transfered my SIM card and tmobile card thing to this galaxy note 3. (my old phone was also Galaxy Note 3)
Now the signal almost always show as 0 bars or a stop sign. And I have not had data working pretty much ever, it just shows at E or nothing. It either takes forever to send a message or fails to send at all too. It didn't matter where I went, my house, school, stores, etc.
However, I went to my father'a house and everything suddenly worked fine. It seems like that entire city my phone worked fine until I came back to my town.
I've never had problems with any phone like this until I switched phones
Read more: Galaxy Note 3 only has signal / data in one city?