Using Mac, can't make outgoing calls

[Adroctheviking]

I've seen some troubleshooting on this issue for PCs, but I'm having this issue on my Mac:

I can receive calls fine, but when I try to call out I hear nothing but silence. I've tested this many times by calling my cell phone (which has very poor reception where I live, my reason for getting a MJ to begin with). I've spoken to tech support and they've had me do everything from trying different USB ports to erasing my software and re-installing several times.

I have tried my jack on my roommate's PC laptop, and also on the Windows 7 I have installed on here through Bootcamp. The jack seems to work fine in both other cases, making me think it's something to do with a setting in OSX Leopard (however, I didn't have this problem until just this morning).

I'm running out of ideas...I would just use my Windows, but I need OSX for so many things that it would be such a pain to have to keep switching back and forth whenever I need to make a call.

Any ideas?