Vietnam's mobile phone subscriptions dropped by 45.3 million to 112.3 million in May, according to the General Statistics Office.
The figure represents a record 28.8 percent decline since March, despite the fact that 4.4 million new accounts were created during the same period.
Dinh Tien Hung, marketing manager at leading mobile phone network MobiFone, attributed the decline to the telecom sector's efforts to weed out disposable phone numbers.
Vietnamese consumers have a history of continually buying new SIM cards to cash in on bonus credits instead of topping up a single phone number.
Though the number of mobile phone subscription decreased to 112.3 million, the figure is still considered high given Vietnam's population of 87 million.
Hung said that several months ago, companies began offering to match 100 percent of credit purchased by their users to encourage them to stick with a single number.
"Since suppliers began slashing rates and offering bonuses, phone subscription has witnessed slow but sustainable growth," said Hung.
"Discarding a number after use is common at the moment. It is important for network suppliers to find ways to keep users. The wild increase in phone subscriptions is just a waste of numbers."