I recently received permission to look into Asterisk to replace our Cisco Call Manager system.
I have read into the forum some and read some of the Wiki and I don’t see an easy answer to my question.
Can Asterisk replace call manager and keep the current voice gateways in place?
Or does Asterisk require the T1 cards on the server?
Is there some particular terminology that I should be using to search for on this topic?
Also is the Asterisk book from O’reilly still relevant?
Then get rid of it 
What voice gateways are you using? Are you using T1s now? do you have channel banks? All pots lines?
ANywho Im sure you can use as much or as alittle of your infrastructure you want.
But if people here are going to help you they do need specifics…
At our main site we have a 2610xm with 2 T1 cards, one with twelve channels on the PRI and one with 24 (i think that is how they are configured)
At our two off sites we have 2610xm gateways with SRST services and they use FXO cards for local dialtone.
All gateways have a four port FXS card but I don’t think that they are used for anything but paging over the PA systems.
All gateways are running h.323. The gateway at our main site uses sip to connect to our fax server.
We have a mix of 9740, 7960, and cisco ATA devices.
We do have a cisco conference bridge but I don’t know what model off hand.