Different telephone number on each and don’t send them in staggered sends.  

If you wish to call the owner, you can take the name and address that you've found in public records and go over to www.whitepages.com and plug in the owner's name and zip code in order to see if a telephone number is available.

if someone is borrowing your car and hits a telephone pole, do you split the costs for the damage or pay for it?

You can ask the court to either decide the matter based on the written record that you submit, or to allow you to appear telephonically -meaning you do not need to go to Virginia for the suit.

I tried a lot of the free resources and most of the numbers are not working.Look up “National Cellular Directory”, they might have what you seek. 

Assets identified in this study include:Appliances: Dishwashers, laundry machines and refrigeratorsElectrical and communication systems: Specialized equipmentCabinetry, Countertops and shelvingInterior Finishes: Laminate flooring, carpet, and decorative elements.Security and communication systems: computer connections, alarm systems and telephone connections60.8% of the total depreciable basis was classified as 39-year class life.

If you are too far away to have driven there, this sounds like a problem which could have been diagnosed and solved on the spot via telephone. 

WiFi or cellular systems can be expensive to keep connected and seem more likely to lose their connection if there's a power interruption or something resets the router. i am looking to purchase a system that works with a phone line.

You could always use a second number or telephone for business, i'd say it's a personal preference & may depend on the personality of your tenants.

They have had a lot of success using the good old-fashioned telephone systematically.