Sorry for the lame question, but i haven't ever succeeded to get a whole picture of all this. I can google, and i do, and i read various articles about asterisk, pbx, etc. Maybe this is not clear for me, because i dont have any experience with "phones" stuff.
So. We have:
PBX station (not Asterisk, but hardware one), which i know should support VoIP if needed.
simple phones connected to that PBX (so we can do internal calls, and external ones through a ISDN i suppose)
What we can achieve with that? Can we have "On Phone" presences in Spark or Dial and Accept calls in Spark? We can install Asterisk PBX in some spare PC with linux. We can install Asterisk-IM plugin, if it's needed to do that.
I dont need instructions how to configure everything. Yet Just want to clarify that thing to myself (and to my boss ).