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.
GSM 06.10 Lossy Speech Compression. A lossy format for compressing speech which is used in the Global Standard for Mobile telecommunications (GSM). It’s good for its purpose, shrinking audio data size, but it will introduce lots of noise when a given audio signal is encoded and decoded multiple times. This format is used by some voice mail applications. It is rather CPU intensive.