There are still landlines in use (although they mostly use VOIP instead of analog phone lines). All cheap cordless phones I know run DECT. It's more than enough speed for speech and more stable than wifi.

The AVM Fritz product line of consumer modem/routers all include a DECT modem for registering extra handsets for voice but they have their own proprietary handsets that support TCP/IP over DECT for things like audio streaming or sending extra media like a caller photo.