That is not exactly what I mean. I am taking about the fobs that work now by just being around your car. How long before that is integrated into your phone. Where is constantly gives off a signal up to say 10 feet. As you approach your car it unlocks. Same with your home. No phone call.
That'd be only slightly more complicated. Based on the need for literally ANY smartphone to work with this I'd imagine it'd have to be through a group like onstar that's "always connected" to your car. And likely run it through bluetooth, unless we wanna chance it running a wireless AP through the car. But that'd lead to timing concerns(how fast the two pieces establish a secure connection and finish the "handshake" process). And require the car and phone both update with a new random encryption key every 24-48 hours for security reasons. You COULD run it through the same process as a vpn key, or game authenticator. But in that case your code is out there in the world for people see/access.
That whole thing is very much already possible. Just needs someone to code for it, and a large group(like onstar) to be willing to take the risk.