Just got this call too. In Vancouver WA. I answered because I use my mobile for work and get calls from all over the country. I answered with my company name. Silence and a hang up. When i called back it rang a few times and discoed.
In Seattle as well. It's great to find sites like this to clarify who called. First call like this to my "work" cell phone. My wife mentioned an 801 missed call on her cell phone a couple days ago. HOW DO THEY GET OUR NUMBERS??? Big brother??