Method for mutually communicating network terminating units using hand-held electronic device

A method for interconnecting network terminating units through a handheld electronic device is applicable in a network system which comprises a handheld electronic device, a computer provided with a network interface and two network terminating units; wherein a user agent in full version is installed on the computer; a simplified user agent is installed on the handheld electronic device; the simplified user agent only has the functions of sending, receiving and processing instructions and can send control instructions to the computer through a network; after receiving the control instructions, the user agent in full version packs the control instructions respectively in two groups of SIP packets and sends the SIP packets respectively to the two network terminating units; after receiving the SIP packets, the two network terminating units mutually send out a connection request SIP packet and a connection response SIP packet so as to establish a connection channel between the two network terminating units automatically, and mutually execute data access actions according to the control instructions of the SIP packets.