I'd try a couple of things to troubleshoot this: Verify if it's a basic wireless problem by associating a laptop to the voice SSID and seeing if you get usable IP. Then, plug a wired phone in on the same vlan that your 7921s are connecting to, to see if it's a problem with the call manager config, tftp setup, dhcp options, etc.
If either of those tests fails, then you know where to look for your problem. On the other hand, if a laptop on that SSID is fine and a wired phone on that subnet is fine, then that limits the potential problems to the setup on the 7921 itself.
Apparently I have checked by connecting laptop with this particular SSID to be connected to the wireless ip phone.
Also I have connected the same vlan to the ip phone and it works .
The SSID is created is so simple . It is open and not broadcasted .
Setting are made by typing SSID as it is , followed by Security Mode which is open , 802.11 which is confusing and I have selected Auto -RSSI to automate the channels and finally single access point which is disabled and power mode which is none.
When I switch on the phone, I get locating network services and followed by connection failed .
Regulatory domains selected is AE and US and channels selected are 1,6,11,13 .