Harpy, any chance you can arrange for one of those Panasonic or Uniden cell-link cordless phones (which hook up to your cellphone(s) via Bluetooth enabling both cellphone and Landline calls to be handled via the same expansion units)
something like, or similar to this one
Amazon.com: Panasonic KX-TH1211B Link-to-Cell Expandable Bluetooth-Enabled DECT 6.0 Phone System: Cell Phones & Service
something like, or similar to this one
Amazon.com: Panasonic KX-TH1211B Link-to-Cell Expandable Bluetooth-Enabled DECT 6.0 Phone System: Cell Phones & Service