Is there anyway to stop the FaceTime ringtone heard on an outgoing call? I have tried the iPhone mute button and FaceTime mute icon with no success.
No, this is not possible without switching output device to another connected device which is muted, such as a bluetooth speaker or car stereo, or jailbreaking to delete the audio file from the filesystem.
You can't actually mute it but you can reduce to a very low level, simply with the volume buttons. It will remember your settings for future calls.