CornerStone Telephone Co. Share: Telephone Services CornerStone Telephone Co. Visit Website Request Info P.O. Box 509 Troy, NY 12181 (866) 240-1912 Trade for FAX line (845) 469-9305 (fax) Facebook About Map About CornerStone treats all of our customers like VIPs, because our businesses depend on reliable phone and network performance. We have a team of specialists ready to help you with service requests, order What's Nearby? Distance: 5 10 15 20 25 50 mi.