Although the Facebook app on the iPhone allows you to use Facebook chat to your friends, the Android version doesn’t yet (annoyingly). But, there’s an app that can help.
Vonage is an app for Android or iPhone, which allows you to chat to or talk to your Facebook contacts. Its free from the App store on Android or iPhone and has voice and messaging functions – like Skype. The difference is this integrates with your Facebook contacts and lets you communicate with them.
To make a call to your Facebook friends they will need to have Vonage installed, but you can chat with anyone that is logged into Facebook.
It works over 3G or Wifi as well – just watch your data allowance on the free calls.
Link – Vonage