This one did the rounds at Chester festival just gone .
Performer goes to the toilet before going on stage for the necessary, sits down in the booth and then hears a voice saying, Hello how are yu, after a pause the artist says I,m fine thanks ,voice says well what the hell are yu doin in there, artist replies , Its fairly obvious what i,m doing, voice, sorry mate i,m gonna have to call you back as some prat keeps answering my telephone conversation.....