Spotty at best. "Furness Creek" seems to be your best bet for coverage, though it depends on what network, roaming access, etc. But, then, Death Valley's beautiful vastness will keep one away from the internet, even if you should need it.
Coyotes and Dingos Oh My!
We grabbed the opportunity to camp in the MacDonnell Ranges in Australia, taking one of several weeks break from our hop on hop off semi booked bus tour. We found an economical car rental, and picked up a tent at the local pawn shop. We spent an amazing week hiking through a national park with nobody there except the dingos and flies. We never saw another person the whole time we were there. The scenery was amazing. We always positioned our tent for a quick getaway to our rental-car just in case the hundreds of dingos attracted by our cooking got ugly.