This attribute specifies the voice law to be established for the IWF
to PSTN modem link for calls established by this
TdmaIwfCallServer. This attribute has one of the following values:
aLaw: A protocol for encoding voice-band audio, Pulse Code
Modulation (PCM).
muLaw: A protocol for encoding voice-band audio, PCM.
Note that this value must match the voice law used at the DMS-
MTX connected to this TdmaIwfCallServer.