Christcorp: Thank you for the thorough response. All I'm saying, really, is that when I call said number using Voipo, I don't hear any ringing. I just get silence until the other end picks up or goes to voicemail. When I call the same number using Callcentric, I hear ringing until the other end picks up or goes to voicemail. I bypassed the router and ATA just to show that it was not specific to those devices.

Since this is only a minor annoyance and, as you mentioned this is new technology, I didn't bother writing a ticket. I saw this thread and thought I'd share my experience.