Now that BitcoinNordic.com accepts payments using CashU, and UKash vouchers can be used to fund a CashU account, this may provide a method for purchasing bitcoins in Vietnam. At one time, Vietnam was one of the countries shown on UKash's website though now I can't see any references to it, so perhaps it no longer is (or never really was) offered in Vietnam.
Is UKash available in Vietnam?
Also, I happened to notice this article about a crackdown there on mobile phone users, requiring a verified identity.
"Police check on 5m mobiles"
"[The reason is] an attempt to rein in the number of subscribers, many of whom have more than one phone so that they can take advantage of special rate deals.
However, a senior policeman, Major General Nguyen Cong Son, said many criminals took advantage of mobile phones for illegal activities, including sending hundreds of messages "scamming" for reply fees,"
I'm curious what a reply fee is.