415-820-9958 belongs to a debt collector - United Recovery Systems - just as other people have posted as well. Aggressive, and they leave you a voicemail with a number to call back - 800-326-3446.
In the one week I installed a new land line, I have received 8 calls from this number. No messages. (I cant even remember this new number - I have to call myself on cell phone to get it to register for DoNotCall.gov)
Yep-- I had these creeps call me several times today too. I called them back to see who they were-- but when they wanted info on me? I knew that their number was criminal. I just called them with *67 and told them to call the SFPD, at the Tenderloin Police Station [lol]