The SIP Number Portability System disables the cellular radios in the wireless device and enables a WiFi 802.11 protocol-based radio. In the airborne mode, it activates a call forwarding registration process which has calls to the subscriber's publicly available phone number forwarded to the Airborne Session Initiated Protocol client through a SIP-based Public Switched Telephone Network access number and incoming communication sessions directed to the subscriber's wireless service provider user address routed to the Airborne Session Initiated Protocol client through a SIP-based data gateway on the Internet or the Public Switched Data Network. On outbound calls, the Airborne Session Initiated Protocol Client populates the Calling Number field with the wireless subscriber device phone number so that the caller ID display located at the called party's subscriber device shows the subscriber's publicly available phone number.