Hi we have just had BT VOIP system installed and did have an external bell installed that no longer works and need to have something connected to the system to allow this would the Fanvil ATA GA 10 work
The Fanvil ATA GA10 converts an IP (VoIP) line into analogue so you can use devices that still use an analogue connection. If its going to work or not it will depend on the type of connection used by your external bell and the way it workd, for this you need to contact the manufacturer of the bell, last but not least, you need to make sure BT will also allow its use.