That wouldn't work with my side, half the time the Pre Call number isn't even a number to reach the sub.I always do a pre call before I leave, just to avoid getting there with nobody home.
If I get voicemail I leave a message that I'm not coming out until I speak to them and say something like as if I don't hear from them I'll reschedule the job.
Usually get a call back a few minutes later.
Other times the Pre Calll number isn't ANYONE that even knows them or anything that is going on.