Somebody asked me this the other day and I though I might as well post it here:
If you loose your ADSL configuration (or buy a new router), the quickest way to get your configuration details from Telefonica is to call 900 502 010 from the telephone line your TelefonicaADSL runs on.
You get through to a Stephen Hawkin style computer that tells you your Telefonica ADSL configuration. Have a pen handy. It’s free, so you can call as many times as you like. Again, it only gives you the Telefonica ADSL configuration for that line you’re calling from.