GPRSPRIO parameter controls whether preemptable ODPDCHs will be treated as idle or busy.
This range is from 0-15.
At a 15 I believe that it will treat your GPRS TS as busy, thus giving you less voice capacity.
If you move it to a 0 or a 1 you will allow gprs to be prempted for Voice. I believe this is used for HR packing.