It would depend on where you are. Here in Utah my cell service goes out within the first 5 minutes of the hike I do by my house. The hike itself is about 2 hours in and an hour out.
Hereabouts, I don't get mobile service on most hikes, but I do get it on many trailheads. So, at the very least, it would tell them which trail I was on when I disappeared.
This may be a thing that is specific to local conditions, though. It so happens that I live in upper Snoqualmie River valley, which has trailheads for many of the best and most popular hiking trails in the area. So, naturally, this is where most of my hikes are. And the towers that provide signal for the towns in the valley are on the surrounding mountaintops, so they provide coverage for a good chunk of wilderness around, as well.
