It seems that the ETSI (which is in the 3GPP to define the standard of GSM) has made a mistake : the algorithm used in DTX is not compatible with the AMR. The voice quality is seriously degraded when AMR + DTX are used together (but not only in alcatel ! it is an ETSI mistake)
Please confirm that with Alcatel first ! Confirm that the problem still exists in your release, and if it can be fixed with a patch.
Haven’t you done a drive-test to hear it by yourself ? I’m sure you would really hear the proble. It is real and not just due to bad measurements…
Let me know 🙂