Ok, I've looked back over a week and saw that this was brushed over lightly in a previous post, buy haven't seen this addressed head on. We all know there was a an update released July 8th. MR2 update.
I have been trying to get it for over a week now and EVERY Time I checked for updates, my TB said "Service Unavailable". It didn't matter whether I was in 3G or 4G coverage. So today I forced my radio to CDMA ONLY. Low and behold it said firmware update available. 73 mb.
So grab a radio switch from the market, any one will do. Out your phone in CDMA ONLY and check for updates. The only catch is when you Accept the update, put your phone away for a couple of hours. Take no calls, don't even breathe on it! Let it finish the update. Then turn the radio back to default.
This worked for me... Not saying it's an end all be all fix. I live in the Phoenix area and have awesome 4G coverage. Maybe it'll work for some of you out there.
I apologize if this was addressed head on like this already.
Feel the thunder w/2750 mAh! Use it like it was designed to be used!