[phonehopper]

You kind of answered the question yourself a little bit there I would start by maybe trying a different phone on your number - to narrow down if the problem is in the device or the network. Chances are you will receive your calls fine. Without really looking too in depth into it, this sounds like the paging settings on your phone (the mogul) are not setyp correctly. There are several handshake pages that need to go through when you get a call before your phone starts to ring. Depending on the results of these pages, the network will decide where to send the call - the phone or whatever other method is setup (VM / system recording etc).

Also, you could try finding the official ROM off a SPRINT phone and flashing yours with that ROM or maybe even flashing it again for giggles. Maybe you had a corrupt write somewhere that is causing the issue ? To me this sounds a lot like an RF setting within the radio itself.