[Asterisk-Users] Connecting Multiple Asterisk Servers!

[Adnan Ahmed]

William,
Thanks friend for your reply we have following setup:
ipphones-->router---->asterisk server with channel bank loaded with
Quad T1 card, also on channel bank several analog phones connected
we deploy these setup at our headoffice and other branch offices
situated in different cities we use TDM400 cards.
Basiacally what we want to do we made our organization own internal
network nationwide provides ivr,voicemail,call transfering,call
waiting.confrencing etc.
possible solutions are:
--->we connected   these servers through IAX
--->we Implement DUNDi using IAX/SIP
--->using asterisk+SER but not sure how?
which one will be a best and scalable solution any
suggestios,tips,guidelines etc

Thanks In Advance.