I was once fucking a rather trashy WG cowgirl style, and her phone was beside us on the bed. When it rang she looked at it, said 'Oh its my boyfriend I've got to take this' and answered the phone, chatted for a minute or so then rung off, carried on shagging me throughout, never missed a beat! I was so surprised I said nothing at the time, and because she was a really good fuck I let it pass.
But ever since then I have always insisted that any WG I see turns her phone OFF at the start of the session.