> There exists a species known as "POTS Replacement" router.
>
> It refers to, in effect, a cellphone that you screw to the wall; it has an
> RJ11 jack for a POTS phone. It's used where you can no longer order a POTS
> line from the LEC, such as in much of Verizon FIOS territory.
There are VoIP adapters which are able to connect POTS instruments to a VoIP access. They're almost certain to cost less than a cellular adapter.
Of course, I'm asuming that you have Internet service and would keep it no matter what the cost of each option.
Bill