Depends on where they are at- too far out in the country and there may be no roads or airports or even fields nearby enough to make anything but a crash landing.
Here in NH and over in VT, cell service is spotty, to say the least.
More often than not, there is none. We have to wait until we are near a town, or sometimes IN it to use our cell phones if we need to.
It would not surprise me if they had poor coverage.