I think DV and then PFD are the best option. DV first so you can see all the charges and figure out what you are up against. Then when they respond do a PFD. Use the template here on the forum, but modify to explain the situation. Were you ever notified by the phone company that this account was in trouble BEFORE they started reporting it? If not, you should state that in the letter, something like "as a co-signer on the account I would have expected to be notified of any account issues so that they could be resolved prior to damaging my credit.... blah blah" then tell them you wan to pay it to get it off YOUR reports. If they still want to leave it on hers, fine. 52 points... ouch.