Sounds like you bought something like we have. We love them!! Only once in June '00 did we have someone else on our channel. (We used our daughter's birthday as our back up channel so if we did switch we knew which one to go to without announcing it.) It's true, they don't reach park to park. But we were able to talk to my dad in the parking lot at MK from Tomorrowland. It does depend on how many large objects are around.
TIPS:
If we were splitting up we would designate a specific time to call each other then meet up. Also remember to turn them off when on rides and in shows.
Buy rechargeable batteries...they're cheaper in the long run.
Always push the call button and wait for your party to reply before you start talking.
(Some have said they have trouble hearing the call, but we never did.)
Put your name & resort on the radio in case you lose one.