Networking phones/switchboard

Hi

Where do I get strated on networking phones?

I've got 10 phones say, and I want them to have individual numbers that can be called from outside:
777 0001
777 0002
etc.

from inside, to contact another internal phone I just dial the extension:
0001

I don;t know what to search for on google, switchboard or something but they give products and not how the whole systems works, how you would set it up yourself. BT (British Telecom) have quoted £1000s to this set up.

Thanks!

http://www.nwc.com/1411/1411ibg12.html ?

http://comm-links.co.uk/index2.htm