Define Dangerous (Score 3, Interesting)

I suppose it all depends on what you consider to be potentially damaging information. You may not be able to run up my credit card if you possess my account number with my cellphone company but you will have access to information I consider private. Imagine, for example, an employer suspecting you of having contact with a rival company. It would be possible, with information other than your SSN, to obtain copies of your call records. I would consider this a breach of privacy and potentially damaging.
I expect (though I don't always trust) any company I give my personal information to keep that information private no matter what that company perceives the potential damage of that information to be. The bad guys are often more inovative than the good guys and who knows what they can do with any given piece of data?