The EnGenius DURAFON - SIP Durable, Long - Range SIP Cordless Phone System is engineered for environments where long - range communication is essential. It provides a secure wireless signal that can cover up to 250, 000 square feet and penetrate through 12 floors indoors. This system supports the SIP protocol, allowing for seamless integration into existing VoIP configurations. Once set up, it can handle up to four simultaneous SIP calls or a combination of three SIP calls and one PSTN call. The integrated 2 - way intercom feature enables instant, private communication between users on the network. Operating on a secure 900 MHz frequency, the DURAFON - SIP ensures that calls remain confidential while its rugged design makes it suitable for harsh conditions.