Roaming problems... full signal, can't make/receive calls

[jlaw]

I've had this problem for a while but have been lazy about resolving it because I rarely roam.

I have the phone set up to "Allow Roaming." When I'm Roaming, it displays Digital Roaming and shows my signal. However, every call I try to make connects, rings, and I get a message along the lines of "Welcome to Verizon Wireless. Roaming is unavailable blah blah."

I called Sprint and they are clueless. They said my account is properly configured. Any ideas?