"Reject call with text message" doesn't work for me. Help?

[mstevens]

I've got the box for "Reject call with text message" ticked in the "Advanced" tab of the phone settings, and there is a message in the box.

The only problem is that it does nothing.

I have no problem sending texts to my son. I do it all the time. Earlier today he phoned while I was with a patient so I had to reject the call, expecting it would send a text saying I'd call in a few minutes. However, he never got the text. We've tested it several times since with the same result.

I'd prefer not to install another app to make this work, and I don't need any additional functionality; I just want a default text sent when I reject an incoming call, not when I fail to answer.

Is this a known issue? Does anyone know of any settings that need to be tweaked?