Like others on here I have had the same problems happening for months (includes troubleshooting). Long story short Tech support reprogrammed my data connectivity on their end didnt fix it, sent New SIM cards didnt fix it, New Thunderbolt phones with new SIMs didnt fix it, and many factory resets in between each step that didnt fix it. Yes each of those steps were each done multiple times. Finally they just said, let us send you a new different phone of your choice. That seems to have erradicated the issue. It sucks that you have to change phones, but it seems that is the only fix even tech support can find.