This should be fairly easy to test. I doubt it is a problem with your wiring as you get a tone, but we can test this anyway.
I'm not an expert, nor do I work for BT. Don't blame me if your girlfriend leaves you and the cat takings up smoking after doing the following.
At this point, you are only interested in the master socket and not an extension. This is the closest place to the BT network you can (legally) test your connection.
First test your phone, either by taking it somewhere else with a phone line, or borrowing a known good one from a friend/family.
Second thing unplug all telephone equipment from other extensions if you have them. You don't know what the previous owners have bodged into the houses telephone wiring. Once you have unplugged all other equiptment test the line. Not working, carry on then.
Now, if you have a new style BT master socket:
Unscrew the bottom half and remove the faceplate and GENTLY unplug it. Its ok to leave the wires hanging out. Don't completly remove it, otherwise you will need to get a punchdown tool to put it back. Don't worry about being electrocuted, you shouldn't be, unless you do something stupid like bite into the wires.
Now you have a socket on the wall that was under the faceplate. Plug your known working phone into this and test.
If it works, then its either a problem with the face plate or a problem with the extension wiring (but I wouldn't have thought that would affect the master unless its seriously screwed up).
If it doesn't work, then it is BT's problem, as you can do no more call them and tell them you have tested from the master socket.
If you have an older master socket then technically it's property of BT and illigal to remove and replace (the same as removing the rear of the new one). So you can either call them and get them to replace it with a new one and fix the fault, or buy a new master socket and replace it and test it again (at your own risk).
The steps above are easy enough for anyone to do with very little risk to screwing anything else up, unless an extension cable falls out, but you can poke that back in and off you go.
If you remove the main plate from the wall, if you don't know what your doing or have a reference then all you have is a bunch of wires and some holes, then you will have to call BT.
Dan