A first telephone number assigned to the first telephone is cryptographically hashed to generate a first message digest, and the first telephone sends a signal to a second telephone over a communication network, wherein the signal includes the first message digest. The second telephone receives the first signal and searches its contact records to determine whether a telephone number in one of the contact records generates a message digest that matches the message digest received. Then, in response to the second telephone determining that a telephone number in one of the contact records generates a message digest that matches the first message digest, the second telephone identifies the contact record that generates the matching message digest and provides audible or visual output of content from the identified contact record.