Is anot a very popular media container format designed for mobile phones; works with standard CDMA2000. The main difference from other media containers, 3GP, is the lack of support for AAC format audio tracks.
this format was originally intended for voice compression and is able to change the bit rates of encoded audio data. AMR is actively used for encoding and decoding voice while its being transmitted over network channels. The format allows one to consider network capacity and adapt it to channel loads. Due to this, the voice quality is practically undiminished.