Cisco 6861 Deployment Manual page 14

Segment wireless voice and data into separate VLANs.
Ensure that Public Secure Packet Forwarding (PSPF) is not enabled for the voice VLAN as this will prevent clients from
direct communication when associated to the same access point. If PSPF is enabled, then the result will be no audio.
Cisco IP Phone 6861 Multiplatform Phones Wireless LAN Deployment Guide
14