VOIP Toll-fraud prevention in IOS 15.1(2)T and later causes call failures

Cisco has stepped up the toll-fraud prevention in IOS 1.1(2)T and later by rejecting all calls sourced from non-trusted IP addresses by default. This means all inbound calls will fail until the source addresses are added to the trusted listed of addresses.

The trusted IP addresses are configured under Voice Service Voip parameters as shown below:

voice service voip
 ip address trusted list

More info can be found here: