I have a New install os7400 with sip trunking. Version 4.80. Sip trunks are registering fine outbound calls are good. After an undetermined amount of time incomming callers get a fast busy. If you make an outbound call then immediatedly make another incomming call it will ring in and work correctly for a few calls. Then after a while it stops ringing in any you have to make an outbound call again to get incomming calls to ring in. It seems like routing/firewall issue. Just can't fingure it out.