Roamless

Roamless targets travelers planning longer Vietnam stays with its RoamlessFlex product, where unused data doesn't expire as long as you stay on the plan. The carrier also offers 30-day fixed plans that provide predictable costs for month-long trips without unexpected overage charges.

The no-expiration data angle is particularly useful if you're spending 4-8 weeks in Vietnam and won't use all your data every month. You get flexibility without watching a clock, and the 30-day billing cycles align cleanly with typical Southeast Asia research trips and extended visits.