I had a very similar one to this yesterday.

I went to visit my girlfriend for the weekend (she lives about three hours away). As it had been three weeks since we last saw each other, you can work out for yourself what we spent most of our time doing.

Anyway, we were lying in bed, watching a film, and at some point my phone must have slipped out of my pocket (didn't notice). Unfortunately, it's a touch-screen phone, and it was unlocked. I only discovered that it was on the bed and unlocked when the following happened:

We were having sex, and midway through I place my hand down on the bed, and it lands on my phone. Thinking nothing of it, I throw the phone off the bed and keep going. After we've finished, I pick up the phone and realise that it's still on the line to my mother and has been for the last five minutes.

I immediately called her, and she asked my why I called and if anything was the matter (she thought she could "hear crying"). I told her I was watching a film, "must have been that," and ended the conversation as quick as I could. Relief came flowing over me.