If it's 3 secs, the default for the parameter 'interdigit short timer' is 3. You can test by dial the number and entering # after dialing the string of digits to see if there's no delay. If that's the case, you can either make adjustments to the di...
You'll need to run a debug log to see what the unit is sending. Normally in response to Invite, it sends 100 Trying, 180 Ringing and then 200 OK. Then the other side sends ACK and then audio occurs.
Sounds like a NAT issue. You can verify by running debug log. Config for logging at https://supportforums.cisco.com/docs/DOC-9862https://supportforums.cisco.com/docs/DOC-26697
