In order to make phone calls via the Internet one’s device has to be compatible with Softphone software. In example in order to call from a PDA using VoIP technology one has to install Softphone software, in order for it to work properly, PDA has to have Softphone compatibility.
From mobiSIP Android or iPhone: SIP Client iPhone is uniquely designed and developed to add the power of making voice over internet transfer protocol calls directly through the Android or iPhone. It’s developed by mobisnow.