its funny to think this is illegal, yet the government does it to every one of us, without our consent. how fucked up is that?
if you are at the point that you need to track someone, you should get a restraining order. if you are stalking them, you should see a psychologist.
or it could be , i loaned some money to someone who thinks he can hide lol get a life man... u read too many comic books.
Track based on the phone number? Not unless you're the police. Or Google, who usually have access to an Android phone's location.
And this, if possible, would be highly illegal if unauthorized.