Rui CarmoAdaptive Multi-Rate NarrowBand, another GSM-oriented standard for audio files (supported by the T68i, P800 and other modern telephones), also related to RTP and UMTS.
Resources:
- 3GPP:26.101 - Generaly payload format.
- 3GPP:25.415, 3GPP:29.415 - PDU Types (0, 1, 14)
- RFC:3267 - AMR over RTP