I've just realised that I really do sound like a complete Twat while talking on the 'phone. Part of the problem is that I speak at a volume that is much higher than strictly necessary, if there is any background noise (at either end of the conversation) then I tend to over compensate for it and make matters worse. I also call everybody "mate", something that I never do in real life and find a little annoying when other people do it all the time.
I could concentrate each time I make or receive a call and make sure that I'm more "natural", or I could stop recording parts of my 'phone conversations and get myself a pen and some paper to make notes with. I know the second options won't exactly cure the problem but at least I won't have to listen to myself doing a pretty good impression of a Saarf Landon Geezer.