Can you hear me now?

I’ve decided I won’t ask why Sherlock can’t get any bars on his phone in the lab at Bart’s in the first episode, but seems to have no trouble texting Moriarty from the lab in Reichenbach Fall. On the other hand, after two weeks of having to ask “Can you hear me now?” and moving around from place to place to try and get enough bars to reach people while I was traveling, I could see Sherlock on the roof to get a connection…