Do I need to re-register my Vietnamese SIM card and what happens if I miss the deadline?

For Mobifone there's a way to keep your number active without an in-person office visit: send an SMS with text GS50 to short number 9199. The package costs around 120,000 VND, and once activated the number stays valid (in this case until August 31, 2027).

Vietnam is conducting a nationwide SIM re-registration campaign requiring in-person visits to carrier offices, face scanning, and updated passport details — for both locals and foreigners. If your number is linked to a bank account, Zalo, or Grab, losing access could cause serious disruption. If you're abroad for several months, check your carrier's deadline before returning.

Before arriving in Vietnam, fully disable your home SIM in your phone settings — not just airplane mode, but actually turning the SIM off. Even if you ignore calls and texts, your phone can automatically connect to a local network and your carrier will bill you for roaming. A single missed call is enough to trigger charges.

Topping up a Mobifone SIM via the official website may return an 'Invalid phone number' error even after successfully logging in — a known site issue. Alternatives include using the My MobiFone app, visiting a carrier store in person, or buying a top-up scratch card at any convenience store.