Does your phone listen to your conversations and show ads based on them?

It's... confusing. I don't want to believe! *X-files music plays* But I've been noticing that too much to think it's a co-incidence. On the technical side, the power-draw etc. from always on eavesdropping would be noticeable, so I'm not certain how it would work (And yes, I've actually developed mobile phones). My theory is they've just got extremely good at mind-reading, yeah that must be it.