SIP 


[[https://www.youtube.com/watch?v=erICfPV8-Lg|What is SIP]]


[[https://www.youtube.com/watch?v=uTU6-gDQL_E|SIP Devices In A SIP Network]]

[[https://www.androidauthority.com/best-android-apps-voip-sip-calls-wi-fi-calling-internet-calling-87396/|10 best VoIP and SIP apps for Android]]