HTC Sense ver 2.1
Service provider: Verizon
I turned on mobile hotspot (by calling in b/c Verizon says that still can't do it on these phones by just hitting the icon) and then the service was enabled and then I checked the box on the app on my phone. Great, all was working. And then, hotspot seemed to turn off about every 10 or 15 minutes by itself.
I called Verizon, they wanted to either fully reset my phone or uninstall all apps. I said this wasn't an acceptable set of options. They said, well actually hotspot is a device manufacturer issue b/c the service is fine and the hotspot app comes from HTC, so they forwarded me to HTC who basically said the same thing. But, I decided to trouble-shoot on my own. I noticed that every time I went to go turn it back on, it warned me that wifi being on and hotspot being on is not supported, so wifi will be turned off. This was curious b/c I never turned wifi on. So, I concluded that some app was turning wifi on by itself. I went to running apps and killed most anything that I thought wanted wifi, then it happened again. I went back to see which apps restarted themselves. A few of these I didn't need like NBC Olympics and NFL 2012, so uninstalled these, still occurred again. Then, I found what seemed to be a likely culprit. There were 2 apps that I installed to help me find my phone if lost/stolen. One was GadgetTrak. I uninstalled this and hotspot has stayed on every since.
I also disabled 'network notifications' under wifi settings and that may have also been a factor that is now not a factor, I'm not sure.