EMSA in the OKC and Tulsa metros use encrypted P25 audio but that's about it. I guess there are some towns with encrypted P25 audio for detectives. I can't imagine that they'll go to a real P25 system for some time.
Yes Oklahoma is all 800 mhz along the I-44 corridor. Now going I-40 you loose Troop A around Weatherford. and all you will hear is low band to the Texas boarder.