If you're (iphone) sending a message to an imessage user (beeper, or someone switched off iphone) with their phone number, and they're enrolled in imessage, an

If you're (iphone) sending a message to an imessage user (beeper, or someone switched off iphone) with their phone number, and they're enrolled in imessage, an SMS will not be sent and they will not get it. This is hearsay based on prior threads, but I haven't read a word against it.