no internet

We have the same issue.  Going on 4 weeks and over 20 hours on the phone with tech support.  We had a Nokia round grey unit at first which worked for about a year.  We upgraded our plan and the unit was replaced with a black rectangular unit (bad choice we know now)  Since then, we have had intermittent service ("connected - no internet").  We have had the unit replaced twice.  We have 5 bars ("excellent power").  We can see the tower out our window, about a 1/8 mile away.  We have had the "tower reset", the unit "factory reset", reseated the sim card, relocated the unit (we even put it outside where it is colder.  All of this results in the same intermittent service - works for several hours sometimes and several minutes other times.  Here is my guess at the problem:  since we have a very strong signal, I believe the "carrier signal" from the tower to my unit is great, but the "modulation, i.e. data" is corrupted by a noisy circuitry in the Gateway unit, or the "new - black box" Gateway design is more sensitive to noisy signals (modulation data) from the tower.  I think Tmobile has been selling the Gateways like gang-busters and needed a batch of new Gateways quickly.  The "new" vendor tried to duplicate the original design but missed the mark in the "filtering circuitry" in the new design.  I have gotten to a level 3 tech support person who "kind of" understands the issue, but I don't think the issue we are all experiencing has filtered down (small pun) to the appropriate engineering folks.  My current status:  Connected without internet