Q: If you have an iPod touch that isn’t connected to the Internet and another one that is, what happens when you call the one that isn’t connected? Does it work? Does it keep ringing or does it say unavailable?
A: Attempting to call an iOS device that isn’t currently connected to the Internet via Wi-Fi will result in the call ultimately failing, since the other device is unreachable. The caller doesn’t receive any indication of the status of the other device, it merely acts as if the call is ringing. If you let the call ring long enough, FaceTime will eventually respond with the generic message that the other party is “Unavailable for FaceTime.” This is the same message you will receive if the user receives the call and doesn’t answer or even if the user declines the incoming FaceTime call.
Note that the iPod touch will only show missed FaceTime calls that are received while it has an Internet connection, so the recipient will not even know that you called if their device was offline at the time. The iPhone handles this a bit differently since it generally has a cellular network connection; FaceTime calls still require Wi-Fi, but if a FaceTime call is received on an iPhone while it is in 3G coverage, although the iPhone won’t ring, the user will receive a missed call notification.