I have noticed the last week or so that if I am in an area with very weak signal or 3G service, it drops it altogether. the only way to get it back when I am back in a service area is to restart my phone. Sometimes with a battery pull, but usually the power cycling works. The thing for me is, for how much I paid for this phone, it should work correctly all the time, every time. It just kind of makes me mad.
are you rooted, what rom are you using -- if your not rooted are you using any apps like juice defender, etc. explain yourself. you could just be running something you shouldn't be running due to technical difficulty.