[geeks] Interconnect: Cell phone to house phone system

[hike]

What's the name of the device that permits a cell phone to be connected to
a house's phone service.  The house phones would made calls routed through
the cell phone.

The cost of an additional cell phone and line is significantly cheaper than
a landline in our area.  It would be easier (to move & travel) to have such
a device.

If you know what this device is called and/or a good & dependable model of
such a device, please let me know.  Thanks!