I search for
Skype in Android Market application and cannot find it. I live in Vietnam.
Skype publish their app directly into specific country's Android Markets, they don't publish it to the "Rest of the world Market", Vietnam doesn't have its own Market, it uses the "Rest of The World Market".
Skype's FAQ says:
Why can’t I download Skype from the Android Market?
The Android Market only distributes applications in certain countries, so it’s possible that your location isn’t supported. To find a full list of supported locations, please visit Android Market Developer Help.
If you live in a country that's not listed, then you can still download Skype for your Android phone from GetJar.com. Simply search for “Skype” and download it for free.
You can search for Skype on the Android Market or you can download the APK file directly from the Skype website, click here.