Hello, This is just to confirm that if you have a Cisco PIX Firewall sitting between your SIP Proxy (eg SER) and your PSTN gateway (in my case a Cisco AS5350) you need at least version 6.3 of the PIX IOS. There's a nasty bug in versions <= 6.2 which prevents transactions to be correctly established by blocking SDP packets. Maybe this will save someone else time Luca