I can pick up the phone at the front desk, hit 0 and it rings to the operator.
This tells me that Operator is setup correctly as the Admin.
I called the motel with my cell phone, which by the way is a local number to the area i'm in. I wait for the message to play, hit 0, and it rings through.
This tells me the voice mail dial action table is set up correctly.
My wife called shortly after on her cell phone which is an Ohio number, waited for the message, hit 0, and it hung up.
This tells me that it's not anything to do with system programming. You cannot control where a number originates from.
Perhaps, someone with more knowledge can clarify if my statements are correct. It sounds like the DTMF sent by certain carriers are not being recognized as a valid entry or perhaps it's not receiving the tone at all.
