Encode the positive integer (index of the preset message) in the length of the ringing: 1 second before cutting = OK 2 seconds before cutting = Be there in 5

Encode the positive integer (index of the preset message) in the length of the ringing: 1 second before cutting = OK 2 seconds before cutting = Be there in 5 minutes 3 seconds before cutting = No 4 seconds before cutting = ? 5 seconds before cutting = haha ... etc It would be much easier to do between friends (understand they are sending a message, not phoning you) but a well coded application could disable its vibrate+ringtone on ALL incoming calls by say, 3 seconds and the message can be placed in that window (so the user doesn't accidentally pick it up thinking it's a call). There are many ways to do it. A well thought out version can become immensely popular.