This document discusses various types of call forwarding in 3 sentences: It describes unconditional and conditional call forwarding scenarios as well as no reply, busy, and not reachable scenarios. The state transition models show the signaling flows between network elements like the GMSC, HLR, MSC, and VLR when a call is forwarded due to various conditions like absent subscriber, no reply, radio congestion, or detachment. Registration, erasure, activation, and deactivation functions are also covered with regard to managing call forwarding numbers and services.