I believe I found the root cause of the issue. For me if I have WIFI on and make or receive calls then the issue will occur. And like mojomal said in post #5 my phone's cell radio will stop functioning and only a reboot fixes it. So if you want to try and reproduce it just turn on the WIFI and connect, then place a bunch of calls then turn the WIFI and wait, eventually the cell radio will lock up. It really sucks because sometimes the phone will reboot instantly and other times it may set there for hours until I try an use it, all the while I was unaware that I was not able to receive calls or txt.
example... I am at work with WIFI on all day. I receive a few calls then leave work. The WIFI will then go out of range and start searching. Shortly after that (I have a 15min car ride home and the cell radio locks up during that trip) cell radio will lock up, but it will still show signal and 3G and in blue as though I am connected, but you cannot call out and no-one can call you. Once I am home and my phone connects to my WIFI I can browse the web with no issues since it is using the WIFI, but all the while the cell radio is totally locked up.
right now I am currently rebooting my phone or just leaving WIFI off to avoid this issue. So in essence I have a broken phone. I have went to Sprint and no help, I have to pay more money to get it fixed. And Moto wants me to spend money to mail it to them all the while I will be without a phone for about 3-4 weeks in which I will be paying for a cell service I cannot use.
I am currently contacting several lawyers to get this issue resolved, and two of which say I have a solid case for a class action since I copied all the forums with all the complaints and no responses from both Sprint and Moto and gave it to the lawyers. So we will see where this goes. In the mean time try out that WIFI trick and see if it causes your radio to hang. Seems that some do and some don't, but mine does, everytime.
EDIT: I just had a reboot and no WIFI, but I did turn on and use 4G, which I never do BTW because WIFI works better. So now 4G seems to cause it with the same as WIFI. So anything that knocks 3G out of the picture seems to be causing my issue....