Put v1.0.18 of 3CXPhone for iPhone onto my wife's 3GS last night, which is running iOS 4.1 (I personaly use a BlackBerry and have done for years, I still don't think that iOS or Android can match it yet for e-mail/calendar/contacst against an Exchange server). I'm in the UK, and the cellular network provider for the iPhone is 'O2' (rock solid 3G connection), and my ADSL is with 'UK Online' (a local loop unbundled product provided over Easynet/BskyB's network, with my modem/router being a Netgear DG834G). This is what happened in order... # App installed fine with no problems. # Setup to connect to my 3CX v9 with SP4 install in the office. # Connected first time but audio was one way, no audio could be heard on the iPhone. # Disabled Wi-Fi and could not connect, so it looks like O2 in the UK is blocking SIP/STUN ?. # Re-enabled Wi-Fi, changed the STUN server to that of my UK based SIP trunk provider, which they run over port 10000. # App now connects again and audio is now two way, although the quality could be better (but none of the higher bandwidth codecs are available, a licensing issue for 3CX ?). ... so I suppose overall I think it's pretty good, but it desperately needs the 'Debug' option available in the Windows Phone to diagnose problems.