The police in the US can do it. And you don't have to be talking on
your cellphone, it just has to be on. They need the cooperation of the
cellphone company, and that is SUPPOSED to requre a warrant (I
believe). All cellphones sold in US have a GPS chip. This does not
mean your cell phone has GPS navigation. They have sold all of this
because of the 911 desire to locate a 911 caller. But it's another Big
Brother item as well.

If you are concerned about this sort of thing, you really should
contribute to the ACLU. They fight abuse of this sort of stuff better
than anyone.