When using VoWLAN, tunnelling all traffic to the ZD is in my opinion best practice. Did you configure the SSID to be tunnelled into a VLAN?
The ZD will not terminate the VLAN.. it will only bridge the SSID INTO the VLAN. The VLAN must be available on the uplink port of the ZD.
For this to work, you would have to enable VLAN tagging on the uplink port first.
After that, configure DHCP relaying and routing on the VLAN and not on the ZD as you would normally do.
For choppy audio, check for receive quality (both ways) first. First thing i would do is a simple ICMP check by continuously pinging the handset to see if thats stable.
Is this occurring continuously or only during handover or in specific areas?