A long time ago my company flying club taught one of our cabin crew to PPL standard.I remember as a PPL examiner filling out some form of assessment for the CAA to to confirm his stammer was not affecting use of the RT.I was able to do this as the gentlemans stammer did not present at all in his use of the radio.Last I heard of him he was a 757 co-pilot with a UK carrier.I believe he used to give talks to support groups for this condition and how it could be overcome and also apppeared in a TV documentary on the subject.Inspirational!
regards Stampe