Bear in mind that a lot of area codes, mine included, are in the form of 01xxx xxxxxx, or in some places (one in my area code for example) 01xxx xxxxx. the 01xxx xxxxxx is something like 999999 numbers, but 0xxxxx and 1xxxxx are probably reserved because service codes exist on it. In my area, 5xxxx 6xxxx 7xxxx are the local town, 8xxxxx are the outlying villages, the town again, and VOIP, 9xxxxx doesn't exist because of 999. I doubt you could dial into a switch nowadays, (there are probably people who could prove me wrong on this, Fone Ranger probably), as BT would have them connected to some internal network not accessible by the PSTN where they can configure their switches. Engineers could use a GSM/GPRS card in a laptop whereby they could access BT's network and configure that way if they needed to (again, I don't know enough about the BT network today to tell you fact). There was a page detailing the BT network from phone to exchange, and BT wholesale has a good section on how its PSTN, ADSL, SDSL networks operate.