This is a third-party research firm that handles VOIP office phone system solutions. If you sign up for some VOIP newsletters that require giving out your pbone number, you'll get a follow-up call from them. I did that last night and got the call this morning. They didn't leave a message in my voice mail, so I called back to see who they are. Had a short chat with them. Not scammers.
This is either someone that can scan Skye numbers, which I just signed up for, or my cell phone services provider, and is trying to sell me call blocking services. This number and 415-229-7568 have no other purpose then to harass the user to buy call blocking services. There is pattern here. The provider introduces the services they want to sell (this is how Caller ID, Privacy Manager, and others became so popular), and so they hire these companies (this particular one is located in SF) to call phone numbers via a scheduled, automated system. Solved this on my land line by purchasing Panasonice equipment that blocks unwanted calls, because the land line services provider was the one initiating the harassing calls, to sell call-blocking (packaged with some other services) and thus drive up my monthly bill and their revenue streams...This explains the wierd response when they are called, they don't really care if you call them, this isn't their purpose in life...