The PS Vita already has voice chat and text chat through its built-in Party application.

CNN: Skype app for PS Vita announced

In 2008, the company launched YY, a voice-based gaming communications service, which enabled gamers to voice chat over the Internet and text chat in real-time while slaying monsters or coordinating gaming missions.

FORBES: YY.com: China's Unique Real-Time Voice And Video Service With A Virtual Goods Twist

Skype works very much like an instant messaging program, but allows users to call people on their buddy list and have a voice conversation instead of a text-based chat.

FORBES: Magazine Article

Customers can initiate a BBM Voice call directly, or instantly switch from a BBM text chat to talk, and back again.

ENGADGET: BBM 7 beta is open now, adds Voice feature for free calls over WiFi