I've been tinkering with 3cx on my home server. I have Windows Server 2003 and a Linksys RTP300. Incoming calls are working fine for audio, (not faxes yet, working on that). My problem is outgoing calls. It will ring on the outside line, but when I pick up, there is no audio. I have seen some other users mention they have an RTP300 working, but can't find a good DIY setup on them. I have used other setups for the Sipura and NAPAP2, but there is still something missing. I'm not sure what logs or settings you would need to diagnose the issue, so please let me know and I will post it as soon as I can.