Some providers offer full service, and some are hunters who will hunt your hogs for free. Some advertise larger service areas than others. I own property in Texas which is why most of these providers are in Texas.
Be careful in choosing hunters, as there are horror stories. But there are many respectful hunters who simply are offering a win-win situation.
In my opinion, hunting must be combined with trapping. Aerial hunting, though expensive on a per-hour basis, appears to be cost-effective. See my page on cost-benefit (click below).