One day, I found that I liked the "phone call during sex" bit. Expanding on that, I like dialing in on the innocuous events of the people being cheated on, before bringing focus back to a scene like this.
The reasoning behind this is a little complicated to describe well. In essence, the idea that this is "bonus sex," or rather, something that's not supposed to be happening, contrasted against events that ARE supposed to be happening...it's a turn-on.
Whether it's Flin's phone with his girlfriend calling, or Julie's phone with her husband calling, I leave up to interpretation.