Call transfer:
user A calls user B
user B answer the call and start talking with user A
user A press transfer and keep user B on hold
user A dial User C and start talking
user A transfer the call to user C
user B and C is talking now and user A exit the call
Call divert:
user A calls user B
user B without answering the call, transfer the call to user C
user C IP phone is ringing and user C answer the call and start talking with user A
Call forward:
user A calls user B
user B configure CFU (unconditional call forward)
user B IP phone is not ringing so he doesn't answer
call forwards automatically to user C and user C IP phone is ringing
user C answer the call and start talking with user A

