Not sure about not using the ADSL bit, I suppose it’s possible, don’t connect the ADSL side of the router.
Other routers I have heard talk of include those from Intertex in Sweden, they are SIP aware and I believe they have a lot of different types available.
I know Draytek is planning an upgrade for their 2600V series to make it an FXO one. Don’t have any timescales though.