What should you do to solve this problem especially when you travel to Vietnam???
The answer is very simple. Just buy a local Sim card!!!
It is very easy to buy a Sim card in Vietnam as you can find it at nearly every shop at a very reasonable price: 80.000 VND(about 4 US Dollars). Once purchasing the Sim card, you can press the sequence *101# to check the info on credit and expiration date. Normally, you will receive a message shown a bonus of 50.000+50.000 VND for making calls and for texting. International calls are pretty cheap, around 4.000 VND per minute, direct dial.A Sim card normally excludes any data and you have to register by sending an SMS to the wireless provider, however, this is not a big problem as you can connect to the internet through free Wifi which is available at every hotel/restaurant/shop.
If you use all the credit in the Sim card, you can buy the scratch card at any shops to extend. The card costs 50.000VN, 100.000VND, 200.000VND, and 500.000VND.
Among many Sim card sold in Vietnam, you should choose Mobi Fone and Viettel – the biggest wireless providers at the moment as they won’t spam you with SMS every hour.
To be suitable for the local Sim Card, you should also bring an unlocked phone GSM compatible and be swapping SIM Cards. An old spare mobile is always preferable even it can’t help you to connect to the internet.
If you bring a smart fone which requires a Nano sim card, you should show it to the sellers (as most of them can’t speak English) so they can help you to cut the Sim card to fit your fone.