asterisk users - Aug 2003 - Asterisks integration with pre-existing PBXs

Several people have asked about integrating asterisk in a company that
currently has a PBX installed. Considering the capital outlay for most
PBXs, depending on the model and age of the system, most companies do
not want to look at replacement.

So, what should one look at in a PBX in order to integrate asterisk into
a pre-existing PBX? I have read of some systems with T1 interfaces, but
what about a system that doesn't provide for that? Is there some way to
make use of the various digium cards to provide for integration? One of
the chief complaints that I hear is that no one wants to purchase SIP
phone or have to have the telephone that goes with the system, along
with some other telephone device on the desk.

Any answers, and I will sumerize... 

Thanks,

Kim C. Callis