After installing 3CX APP on my iPhone 4S with iOS6 and then iOS6.01 it works wonderful with my PBX as a SIP-Phone. The iphones have one problem: After going in sleep modus it took some minutes and WIFI is switched off, only cellular data is working. Or you can deactivate cellular data, then even this is off and nothing works after going to sleep. It is different while it is charging, then WIFI stays on (cellular data must be deactivated). There is a bundle of complaining... https://discussions.apple.com/message/20273592?ac_cid=tw123456#20273592 3CX APP (1.1.5) seems buggy, because if cellular data is deactivated AND it is charging, a permanent ping to the iphone even in sleep modus shows, that the WIFI remains on. But after some minutes - ping is still successfully running - the 3CX APP cannot be called. It is a different behavior when WIFI is disconnected. The PBX makes busy when calling the WIFI disconnected iPhone, but the PBX is calling without error while calling the WIFI connected but sleeping iphone. If you wake up the iphone then, it suddenly begins ringing, even if on hooked at the PBX. It seems that there is a cut between the iOS and the APP - maybe the fault of apple or the APP. Any idea ?