The New York Times reports on how your cellphone number is more than just a bunch of digits. It is increasingly used as a link to private information maintained by all sorts of companies, including money lenders and social networks. It can be used to monitor and predict what you buy, look for online or even watch on television. It has become “kind of a key into the room of your life and information about you,” said Edward M. Stroz, a former high-tech crime agent for the F.B.I. who is co-president of Stroz Friedberg, a private investigator.