[Backdated to around midnight last night/this morning. Before the Moriarty/John/Emma thread....]
Sherlock knew that this was the end. He had no delusions that he would die after this phone call. It was cruel, but Moriarty had been so certain that John was dead and Sherlock knew he wasn't. So he called. At least they would have a goodbye this time. That was something he was told. Closure. He even put the phone on speaker. Just to prove that it was truly John he was calling and not a random person to pretend it was John.