Providing user notification signals in phones that use encryption

A method for providing user notification signals in digital phone such as IP phones or cell phones that use encryption. In one embodiment, a digital phone receives an encrypted data packet. The phone determines that the encrypted data packet satisfies a criterion. The phone generates a user notification signal that is perceivable by a user of the phone in response to determining that the encrypted data packet does not satisfy the criterion. The user notification signal may comprise a tone, synthesized speech, or other signal that is audible in a handset or speaker of the phone. Alternatively, the user notification signal is visually displayed in an electronic display of the phone. The criterion may comprise a failure to authenticate one or more encrypted data packets that are provided to the phone in a secure protocol. The process may be performed at a voice gateway or cellular base station.