If your looking for network reference information (voice, data, video, LAN, WAN, Mobile, signalling systems International specifications etc) look no further. The following sites have heaps of information to keep you busy for hours (many erlangs worth!!)
Enjoy
The Telecom Bible! – http://china.si.umich.edu/telecom/telecom-info.html
Detailed information on British Telecom (BT) Services
http://www.sinet.bt.com/sinlist.htm
http://www.sinet.bt.com/tiglist.htm
http://www.sinet.bt.com/spinlist.htm
General telecom info
http://www.landfield.com/faqs/uk-telecom/part1/
http://www.electric-words.com/dict/dictfrm.html
http://www.jtec.com.au/papers/index.htm