If you need VoIP application that is portable, can be bring anywhere, I suggest you to use this Skype 5 beta portable edition for Windows. This is unofficial portable edition of Skype. You can download this Skype portable from the link provided below this post.
Skype has launched a new version of its iPhone application that, for the first time, allows iPhone users to make and receive calls over their 3G data connection, but it will start charging for Skype-to Skype-calls.
Skype has released an upgrade to the Skype for Android app (2.0) that supports video calling over Skype to Skype contacts on other Android phones, the iPhone, Mac, Windows PCs and Internet connected TVs.