ta.
I usually go for 568B, but I have come across some kit only marked in one flavour or the other. Hence its probably better not to specify and go with what matches what you have.
phones as well... Perhaps its more accurate to say that the pin 3 "bell wire" is not usually carried over the structured cabling, but is not always required either.
I did look at the possibility, and compared to an Avaya or other similar modern digital exchange it costs very little. However by the time you look at the cost of a 16 port card, a PC (which to be fair I could scrape together for nothing), and the power to run it, its quite expensive compared to an analogue 4/16 PABX direct from Hong Kong.