Add calling and texting options to iPad 3G over regular cellular networks.
iPhoneIslam, the group that brought FaceTime video calling to iPhone 3GS have now brought a brand new app to iPad, which enabled regular phone features via your iPad 3G. Thus aptly called the PhoneIt app. Apple doesn’t support this app so you will need to use Jailbreak your iPad to use it then you can purchase PhoneIt app from Cydia for $20 and thus convert your iPad 3G into a giant iPhone, enabling cellular calling and texting (SMS).
Even though iOS5′s iMessaging will enable texting but only from iOS to iOS. But this app will enable call and messaging across regular mobile network.
Get the app @ Official site