SRD:Correspond

You forge a passive mental link with a creature with which you have previously had physical or mental contact. The subject need not be within sight or even on the same plane as you are. The subject recognizes you, and you can mentally communicate with it for the duration (though nothing forces the subject to respond to you), exchanging messages of twenty-five words or less once per round. Receiving a message is not an action and does not provoke attacks of opportunity; however, sending a message is equivalent to a standard action that can provoke attacks of opportunity.