If you have a BT phone or a near neighbour has you can check the line length using details from
http://www.the-scream.co.uk/forums/t181.html
Hmmm, having read through the thread that I posted the link to it appears that this may no longer work. It did a couple of years back when I had a BT phone and tried it but only having a NTL phone now I can't check. Possibly it was being over used with people wanting to check their line length for broadband and BT now have a different number for the checks.