The hardest parts of it will be to configure:
[ul]Proper call flow to go out from the switch to the T1 in the Asterisk machine.
MWI signalling, if you want the phones to “light-up” or do stutter dial-tone when the handset is picked up.
[/ul]
The rest is just basic asterisk setup. (Though, I like to use a real-time mysql database)