I had recently upgraded a Cisco UC520 device to the latest software revision, version 8.0. It ran well for about a week then yesterday we had to reboot the device due to a locked DN. Upon rebooting the device the CUE loaded but when dialing the AA or voicemail system nothing but dead air was heard then eventually a busy signal.

To resolve the issue we had to un-configure and reconfigure the Intergrated Service Engine settings.
*The fix below has been modified to reflect the default configuration.

Router#config t
Router(config)#interface IntegratedServiceEngine 0/0
Router(config-if)#no ip unnumbered
Router(config-if)#no service-module ip address 10.1.10.1 255.255.255.252
Router(config-if)#no service-module ip default-gateway 10.1.10.2
Router(config-if)#end

Then remove the default route for CUE:

Router(config)#no ip route 10.1.10.1 255.255.255.255 IntegratedServiceEngine 0/0

Finally, add all these commands back under the interface and the default route.