Configuration Problem

I’m kind of new to Asterisk so bear with me.

My company is trying to get a cheap PBX system up and running using Asterisk and Ubuntu Server. We’ve purchased 2 SIP trunks from, but have had trouble trying to configure them. I’ve used the asterisk-GUI to add as a service provider using their preset settings, but whenever I dial out it just sit there at “Calling trunk_1/+MYCELLPHONENUMBER”.

When I try to call in with my cell phone, it gives me this error:

NOTICE[5217]: chan_sip.c:13952 handle_request_invite: Call from ‘’ to extension ‘+OURDIDNUMBER’ rejected because extension not found.

UPDATE: After showing this error, and after a long silence, my asterisk phone will ring, but as soon as I answer, i get a busy signal and the phone hangs up.

So I know my SIP trunk is hitting Asterisk, but my configuration must be wrong. I just don’t know what it could be. Any ideas? Thanks.