As another poster said, it's certainly physically possible to do. Messages can be sent electronically to the cockpit over ACARS. The pilots can then print it out and give it to a FA to deliver to the pax. Whether you can reach someone at the airline willing to do that is another story. If you're expecting to need to communicate with a pax, you can have them setup the satellite phone to receive incoming calls on many international systems, though you'd need to arrange that with the pax ahead of time (and making and receiving calls isn't cheap).