Believe it is an automated service known as Message Forwarding where instant messages from people are sent to a system where an Operator calls you and relay's the message over the phone. You then have the option to reply via speaking to the operator and they type the message in to send to the unknown messenger.
Believe it is an automated service known as Message Forwarding where instant messages from people are sent to a system where an Operator calls you and relay's the message over the phone. You then have the option to reply via speaking to the operator and they type the message in to send to the unknown messenger.