Editing Nordic Mobile Telephone (section)

=== Security ===
In the original NMT specification the voice traffic was not [[Encryption|encrypted]]; it was possible to listen to calls using e.g. a [[scanner (radio)|scanner]] or a cable ready TV. As a result, some scanners have had the NMT bands blocked so they could not be accessed. Later versions of the NMT specifications defined optional analog [[scrambler|scrambling]] which was based on two-band audio frequency [[Voice inversion|inversion]]. If both the base station and the mobile station supported scrambling, they could agree upon using it when initiating a phone call. Also, if two users had mobile (phone) stations supporting scrambling, they could turn it on during conversation even if the base stations didn't support it. In this case, audio would be scrambled all the way between the 2 mobile stations. While the scrambling method was not at all as strong as encryption of current digital phones, such as [[GSM]] or [[CDMA]], it did prevent casual listening with scanners. Scrambling is defined in NMT Doc 450-1: System Description (1999-03-23) and NMT Doc 450-3 and 900-3: Technical Specification for the Mobile Station (1995-10-04)'s Annex 26 v.1.1: Mobile Station with Speech Scrambling – Split Inversion Method (Optional) (1998-01-27).