Broken phone?
I installed an ADSL service yesterday and

had a spot of bother that needed a call to Be support for help configuring the modem, anyway, I found I didn't have a dial tone when I tried to phone???
I checked all the connections to no avail and then after a bit of messing with the "call finished lever?" on the handset (the thing thats gets activated when you hang up the call) it came back on? Coincidence or what?
Lines 2 and 5 do carry a current, if you inadvertantly shorted them maybe you have blown something at the exchange?
Try another phone and if that don't work then it looks like biting the bullet and getting BT out.