Configurations of GSM/VoIP networks allow the service providers to avoid the local Wired Public Switched Network (PSTN) in communication with a GMS mobile handset. As a result, the high rates charged by telephone companies are avoided.
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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