I've been getting two or three calls a day from this number for over a week.  I've let the calls go to my voicemail, and no messages have been left.

Same as Mark, I've been getting two or three calls a days as well from this number and never any message.  Since my number is brand new, and I've only given it out once when I wanted some health insurance quotes, I believe this is an insurance agent.

I just received a call from this number as well. I looked it up on http://www.thedirectory.org/pref/
It come back to
Number: (650) 276-0155 Search Date: 04/14/2008 Search Time: 7:12 AM
City: Half Moon Bay State: CA
On Another Web Site It Gives This Information

650-276
HALFMOONBY California
LEVEL 3 COMMUNICATIONS, LLC - CA CLEC  (This is the communication company in charge of that area)

I have been received at least 10 calls a day from this number, 650-276-0155. They never leave a message. I tried calling back and a message says put in the extension number or dial 0 for the operator. If you press 0 than it either hangs up on you or just rings. This is so annoying. But yes, I put this number in when I did the online insurance quote thing as wel. At first another number was calling and they left a message. Then aftere about 3 days of them leaving messages this other number started calling and after a week of calls they are still calling at all hours of the day.

I've been getting calls for 2 months...this is apparently a land line and the provider is Time Warner Telecom of California and yes, my research shows they are in Half Moon Bay which is in the county of San Mateo.  Of course, no one will help me stop this....my cell provider and TW of Ca claims they "can't" help me.  Does ANYONE have any ideas for finding out who this is?  I'm going to call the state police if I get one more call and file a harassement complaint!