Maybe I wasn't clear on the scenario.
This is my current setup
Extension 100
Extension 101
Extension 102
Extension 103
Extension 104
Now I have the following trunks:
Trunk 1 > ex 100
Trunk 2 > ex 101
Trunk 3 > ex 102
Trunk 4 > ex 103
Trunk 5 > ex 104
Now, each line is restricted to 1 (one) line. If someone calls Trunk 3 and extension 102 is busy then the call will be forwarded to 103. If 103 is busy, it will then be forwarded to 104, if 104 is busy it will be forwarded to 100, and so on...
Now my problem is that I would like when I'm out of the office for all 5 extensions to be forwarded to my cell phone number 555-555-555. But at the same time I wouldn't like to press *72 4165555555 for every extension. I would like to use a service flag or something similar to just forward all the accounts on my domain to my cell.