What are the advantages of AMR speech codec over other codecs?

PLease discuss/ provide links to docs addressing AMR-speech codecs concepts.

What are the advantages of AMR speech codec over other codecs?

Wat are the differences between AMR-NB and AMR-WB?

Where are these codecs used?

Re: AMR speech codec

AMR(adaptive multi rate) is a speech coding algorithm used in GSM(optional) and UMTS(mandatory) networks.

An important feature of AMR is its ability to adapt to radio channel and traffic load conditions and select the optimum channel mode (HR or FR) and codec mode (bit rate trade-off between speech and channel coding) to deliver the best possible combination of speech quality and system capacity.

AMR is well discussed in the following book “GSM, GPRS and EDGE Performance : Evolution Towards 3G/UMTS”, here is a link from “EDA & Electronics Related E-Book links” section:
h**p://rapidshare.de/files/24504882/THalonen.rar.html

You can also look through the following technical specifications:
h**p://www.3gpp.org/ftp/Specs/html-info/26-series.htm