This is a device allowing a user to make VoIP calls using session initiation protocol (SIP). SIP is a telecommunication technology developed as a fast, easy standard for delivering IP-based data, voice, and video communications.
VIETTEL TELECOM
Viettel Group is one of leading telecom service providers in the world with over 50 million subscribers. Wireless Intelligence has ranked Viettel Group as the 19 th out of 784 biggest telecom service providers in the world regarding the number of subscrib
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