GPS has always had to account for relativistic time dilation, it's the first human scale issue where relativistic correction became necessary. (This would be general relativity, incidentally, not special: it's the effect of the Earth's gravity on the atomic clocks in orbit.) But that's because the whole system needs absurd levels of accuracy to be useful at all: at 8 km/s of orbital velocity every source of error creates enormous error bars on the ground.

I also know that NASA has experimented for years with satellites (even all the way up in GSO) using GPS signals for position-finding, so this is further out but not unprecedented work.