If an outbound call fails to local numbers or any other number out of the Public Switched Telephone Network (PSTN) gateway, it can be because the gateway sends a bearer capability with Unrestricted Digital. For example:
Bearer Capability i = 0x8890A3 Standard = CCITT Transfer Capability = Unrestricted Digital Transfer Mode = Circuit Transfer Rate = 64 kbit/s Channel ID i = 0xA9839F Exclusive, Channel 31
Telco disconnects with the Cause i = 0x84EF - Protocol error; unspecified error message.
This capability is sent when the IP phone has video capability enabled. If Telco does not support this capability, the call is rejected.
In order to resolve this issue, complete this configuration on the primary rate interface (PRI) voice-port, on the PSTN gateway:
voice-port x/y:z bearer-cap 3100Hz
This changes the bearer capability in the setup message to 3100Hz (for voice).