EnGenius FreeStyl 2 Long Range Cordless Phone: https://youtu.be/rS7kaQVru9I
EnGenius FreeStyl 2, Long range, Expandable up to (9) Handsets, 900 MHz, Scalable Cordless Phone with 2-way Radio for Broadcast or Intercom, Coverage up to 100,000 sq ft (Amazon Affiliate)
US: https://amzn.to/377SOeB