As far as I know, all the major semicondutor companies (Qualcomm, TI, Infini) to work on the GSM baseband IC inplement the AMR in the DSP not the ASIC. It is not a good design to use the ASCI to implement the AMR since the AMR vocoder involves some very compelx DSP algorithms.
What about implementing it in Microcontroller DSP instructions
Like ARM9E .
I found some docs from ARM and some other suppliers claiming that it could be implemented in about 50MIPS on ARM9E
What do you think?