I also have an 8703e from Sprint and was having the same problem. I am now on my 3rd Blackberry....after many hours with Tech support in the store and on the phone, I think it was Yahoo IM. I have now had the Yahoo off of my phone for about 5 days and it hasn't rebooted since...which really sucks because I communicate with alot of people using IM. It's the only solution that I have been able to come up with. Good Luck!