[asterisk-users] Cisco vs Asterisk

[voip crazy]

Hello all,

A client of us, is thinking to migrate their actual PBX to a Cisco
CallManager. We want to sell him an asterisk box to complement the
Cisco PBX.
I think to use asterisk as a Voicemail server (Replazing the Cisco Unity)

Has asterisk all the functionalities to replace a CIsco Unity server?
Which functionalities Cisco Unity has than asterisk could cover?
How could asterisk complement the Cisco Call Manager funcionalities?

Thanks.

VoipCrazy.