Hi, I have built a test PBX with Elastix 1.4RC using an Openvox B100P ISDN card and an Openvox A400P card with 1 FXO and 2 FXS modules. For testing I have been using ZoiPer softphones and analogue handsets on the A400P. My biggest problem has been with very poor sound quality when making calls on the ISDN trunk. The remote party has been able to hear very well but the caller attached to the Elastix system has had very choppy sound quality. Initially it did not matter which extension was used, all were equally bad. Then I found out how to put the analogue card into UK mode and then the quality on the hardphones was fine. Then I tried connecting the ZoiPer softphones with SIP extensions rather than IAX2; they now work fine too. The sound quality on the analogue trunk and between extensions has always been OK so I have wasted a lot of time thinking that the fault lay with the ISDN card. I hope this may be of some help to others even though I don't fully understand it myself yet. So, my questions: How can I get softphones to work using IAX2? (Should I just give up and use SIP?) Why does this only affect calls from/to the ISDN circuit? Cheers, Ray.