We have 3CX Phone System v12, and several Android (v5) and iOS (v8) extensions, as well as desk phones (Yealink T46G and T42G). Our system has a PSTN gateway (Patton SN4316) and a VoIP trunk provided by IrisTel. We are seeing that the iOS clients can not navigate IVRs over the PSTN (pressing keys does not navigate menus successfully). Only iOS clients fail, and only over the PSTN. iOS clients can navigate IVRs if they dial out using the VoIP trunk. All Android and deskphones can navigate IVRs over PSTN or Voip trunk. Is this is Patton issue, or a 3CX issue?