Hi, Pretty new to 3CXPhone and have a question about the RTP ports setting under Preferences. I use 3CXPhone (5.0.14900.0) with 4 external VoIP providers, a mix for inbound and long distance outbound. I've always understood that the RTP ports to forward were dependent on the SIP device/agent. In the case of 3CXPhone, they are 40000-40049 UDP by default. This port range is purposely compatible with the 3CX PBX product. But I don't use 3CX, so I simply forward this range in my router firewall, along with 5060-5080 UDP (SIP). But according to this blog post (http://blog.cqvoip.net/2010/05/3cxphone-softphone-configuring-it-with.html), the correct RTP ports are dependent on the provider! The blogger says they should be in the range of 10000-20000 UDP. He mentions this is definitely the case for provider Callcentric. But in the CC support section, this page (http://www.callcentric.com/faq.php?s_go=1&search=ports&go=Search#226) states that the ports depend on the user agent. It has no mention of a preferred range. The reason I ask is because I'm confused and having call quality issues with two providers that I did not have when using Express Talk. I even asked the provider Localphone for help and they said just to run the router in DMZ mode or turn off the firewall entirely. I obviously don't want to do that. As a side question, do I need to forward the STUN port (3478 UDP) as well?