La Gazza Ladra by Giaocchino Rossini, used for the fight scene in this episode, was also used for the scene wherein Moriarty executes his plan. In both, the music is used to accompany a tightly choreographed and consequential series of movements in a pivotal scene.
Sherlock meets Moriarty on a rooftop, just as Costigan meets Colin. In each case, a character is trying to retrieve their good name/identity. In each case, cell phones are a crucial device.