One thing I found, Try not to use the polyphonic ring tones while in the park. Just use one of the "classic" ring tones that come with the phone. They're usually louder, and don't "mix" with the background noise and music of the parks.
Cell service definately depends on the carrier. Nextel is 100%, inside and outside, all the rides, everywhere. I don't think nextel has a single dead spot on property ( WDW uses Nextel for walkie-talkies now ). US Cellular works decently, just not inside any of the rides. It was always in roaming ( before I switched to nextel), but it always worked. I've heard the same thing for Verison, it works, just not inside some of the rides.