Each cell phone subscriber can only register three numbers, according to a recent decree issued by the Ministry of Information and Communications.
Individuals can use their ID cards or passports to register a maximum of three numbers for each operator.
With six telecom service providers, and Gtel Mobile to start services in July, users can register a maximum of 21 mobile telephone numbers.
From 2010, under a regulation by the ministry, pre-paying users will be cut-off if they do not provide personal information or if they supply false data to providers.
The regulations have been brought after complaints of nuisance calls being made by unregistered phone users.
Vietnam has 96 million cell phone subscribers, with 90 per cent of them pre-paying subscribers.
Telecommunications companies reported revenues of US$5.4 billion last year, up 38 percent from 2007.
