Recently, I have been called in to "fix" broken public address systems after one on my beloved competitors has installed a cloud phone system. The customer was told that Cloud phones and paging do not work together.
Most premise phone systems have a page port that connects to the audio input on the page adapter (or amplifier). Since by definition a cloud system does not have equipment on site, how can you connect a cloud phone system to a legacy paging system?
There are two easy and inexpensive tricks which work well.
1) If you are interfacing with an amplifier - Install an inexpensive VoIP speakerphone near the amplifier. Set up the phone in a page group that includes the phone. Open the phone and cut the speaker wires of the internal speaker. Connect the wires to the audio input of the page adapter or amplifier. That will give you the analog audio input that the amplifier requires.
2) If you are interfacing with a page system where the interface requires a loop start trunk or analog extension: Algo Communications makes a very tricky IP gateway. If you put the Algo box on a cloud SIP station, the Algo has several output options including analog trunk (FXO) analog station(FXS) or page port. The device will also support multi cast paging with Polycom, Yealink and many other IP phones. As an added benefit, you can schedule time based tones. It's the Swiss Army knife of page gateways.
There are many legacy telephone devices that may need to interface with your cloud phone system. In our experience, with a bit of creativity and one of the gateway products available, you can make most of them work quite well.
Gregg Haughton has been selling business phone systems that enable companies to improve productivity, enhance customer service, and lower costs since 1986.