The phone company knows approximately where your cell phone is when it is turned on, based on what towers are receiving the phones signal. They don't give this information out willy-nilly, but if you are planning a perfect alibi, turn your cell phone off, first.
I'm sure phone companies, like everyone else, get hacked once in a while. So, your whereabouts are going to be leaked from time to time, but probably not to your friends and family.
For cell phones that have gps, the phone itself could get hacked, and Google and all manor of semi-benevolent organizations use the gps information to give you location relevant ads, embed the location your picture was taken in photos, etc.
However, when I misplace mine, I usually call it and hope the battery is still charged enough to ring the phone.