0x01 Free System Resources

Used in:

Connect with Data message

ICB Type | 0x01 (Action)
ICB ID | 0x01
Data Length | 0x02
Data[0] | Channels to Free Resources For 0x01 Channel A 0x02 Channel B 0x03 Both Channels
Data[1] | Resources to Cancel or Free 0x01 Digit Receiver 0x02 Transmit Call Progress Tone 0x03 Both Resources

See Information Control Block.
A tone sent to the caller indicating the progress of the call. Examples include dial tone, busy tone, ringback tone, and comfort noise (digital cellular).