Hi, for the modern digital telephone you now only need connections 2 and 5, the connection number 3 is the bell wire required for the old electro-mechanical telephone bell, it is better to not connect this wire as it can cause interference to your broadband connection.

http://www.telephonesuk.co.uk/wiring_info.htm

Wire (B) 48v DC Live.

Wire (A) 0v DC Neutral.

http://www.wppltd.demon.co.uk/WPP/Wiring/UK_telephon...

http://www.rob-r.co.uk/other/UKphonecatwiring.html