I have a PSTN Base that has a couple of 6000's and a 2 attached. I also have a 1401 connected to a separate BT socket in case of power failure.
Problem is when I want to use the base with VOIP. As per a different thread here: https://forum.beoworld.org/forums/topic/beocom-6000-and-virgin-voip/ I have the same problem where an incoming call is dropped immediately (outgoing works fine) and I'm using a Cisco SPA112, the same as @keith_saunders uses though mine is with voipfone.co.uk.
When I connect the 1401 it all works fine so it would appear the base is the problem.
Earlier comments provide a solution when using a VOIP adapter to ensure you're using a 4 wire RJ11 to BT adapter to connect the base to the VOIP adapter. I see that the RJ11 to BT adapters that come with the SPA112 seem to be 2 wire, so I presume these could be a problem? However, my base station cable has an RJ11 to BT adapter on it, so if I remove this I can plug it directly into the SPA112 via RJ11 and bypass the adapter altogether. This doesn't help - same situation with incoming calls dropped. Whilst I see some have managed to get this to work I wonder if obtaining a 4 wire adapter will help when considering I can plug the base into the SPA112 directly?
Are there any settings applicable to the SPA112 to work with the base?
Any thoughts please?