My dad uses Skype to make calls to Vietnam PSTN, but finds that the rates are a little on the pricey side. It's probably not relevant, but he's living in Thailand right now. Is there an application similar to Skype, which is cheaper for calling Vietnam?

The answer may well be no, since maybe the international telecom peers in Vietnam are just generally expensive... Who knows?

While I'm asking, maybe it's worth someone mentioning if there's a cheaper alternative to Skype in general? I'm thinking that maybe not as Skype's pretty cheap anyway, but it's worth mentioning.