A mobile number in Vietnam is registered to one person. A foreigner registers with a passport, so the counter needs to see it.
Since 2026 every number is checked against its owner's papers. A number that fails the check loses outgoing calls and messages. So buy the card in your own name, not somebody else's.
Prices and networks are not printed here, because none of the networks publishes a tourist price page we could read. The price board is at the counter.