LMAO. I'd have upped the tempo from behind.......she would either have had difficulty in continuing the conversation or the person at the other end would have got a right good ear full.
Funniest thing that happened to me was when I was on the receiving end of some very good oral. The escort took a call and was talking away to her friend. The conversation went on for a few minutes as her friend seemed to be conducting a monologue which was becoming tedious for my companion. So with her left hand pressing the phone to her ear, she grabbed me with the right and continued performing oral. Every so often she'd let out of slurpy grunt so her friend knew she was still listening.