Our experience with schools and the fact that there can often be several blocks seperated by some distance always leads to us recommending IP systems.
If you look for an IP system make sure it is pure IP. There are a lot of systems out there that "also do IP" which is very different from being purely IP systems.
If you go for a pure IP system it should have the benefit of distributed architecture. Which basically means that like anything that uses Ip not all the "bits" or "boxes" need to be in the same place.
Why is this a benefit? Well, for example, if you need some analogue devices on the 3rd floor of block D! then rather than having to run cabling back to the comms room, you simply locate an analogue telephone "box" on your LAN somewhere on the 3rd floor, Block D and then only have to run CAT5 to and from that point for the actual analogue device.
As mentioned previously in this post there are a lot of system resellers that only specialise in one or two systems so the salesperson will always try to match their system to your requirements. I think you could do a lot worse than look at the iPECS from LG Nortel. It won't break the bank and it can be administered via an embedded web interface. So simple moves and changes can be done in house with a little initial guidance.
