Two things could cause the phone to not ring or not properly ring:
1) The phone is hooked up to an Internet router and the ring signal provided by the router is not according to standard. Our phones work with most routers on the market but of course we could not test all of them.
2) If you are connecting several phones in parallel to one phone line they shall share the ringing voltage supplied by your phone system. Depending on the type of phone and the phone system at your location this power may or may not be sufficient to drive more than one phone. Modern phones usually require only a small amount of power in order for it to ring. The OPIS phone however may not be happy with whatever power is left by the other phone. If that is the case you will either need an amplifier for the ringer signal or operate each phone at a separate line (number).
In order to check if the phone is fully functional you may try the following:
a) Call your number with an external phone (e.g. cell phone). When you hear the call signal in your cell phone please pick up the Opis phone. Please check if the two are connected?
b) Maybe you can test the phone at a different location. If the phone rings there the problem is with the phone system at your place.