I’m in the UK and will soon need to switch over from the old copper landline to VOIP for my phone use (my property is already on fiber, FTTP to be exact).

I know that I need a VOIP Analog Telephone Adapter (ATA) in order to connect my old analog phones to the router. However, my ISP doesn’t seem to think that I can plug in TWO phones simultaneously (yet only one will ever be used at a time). One is a cordless phone with wired base station, the other a simple wired phone (so not cordless and no base station) which I use in the event of power cuts). Surely it should be possible to plug in some kind of multi-way/T piece adapter to the VOIP ATA to save having to swap cables whenever there’s a power failure. (the ONT box and router will be powered via a UPS).