I know exactly what you're talking about. I've had this problem since the first day I had my i830. I've been told by numerous people that the 830 has the worst reception of any nextel phone ever made. I believe it. My husband and son both have nextel and when we're traveling, I'm usually out of service while they have 3-4 signal bars.
It's the phone and it sucks. I'm looking for a new phone now and at least I know which one not to buy!