[Serusers] Clueless newbie question - integrating SER and Asterisk

Help! I've followed the SER documentation and searched the web like a mad thing and found nothing useful. I have an asterisk box here at home and want to put SER on it so I can use SIP clients out in the real world (on the other side of my firewall) to get to it. Now, I have got SER set up and the phones register fine and everything, BUT I cannot see how to get it to pass calls through to Asterisk. I'm not using Asterisk realtime or anything like that - just plain old asterisk with plain old config files. I thought I had it right, but calls are just not getting to asterisk so far as I can see. I know it must be possible, I just can't see how to do it. Regards John Breen