I'm not sure that's true for dense urban zones like NYC. I'm pretty sure my phone registers with many different towers frequently.
There's a tower on almost every other building in New York, and sometimes even within buildings and underground.
Considering that smart phones are particularly promiscuous, especially in the presence of poorly conceived and opportunistic apps (downloaded by my rotten teenage kids), my phone is probably a shining beacon of electromagnetic activity, constantly transmitting high-score updates, and my entire contact list and GPS coordinates to web servers hosting silly JSON APIs.