I used to have the same problem, until I found a great solution
I bought a Panasonic Phone that has a feature called Link to cell, basically it lets you use your home phone as a Bluetooth device for your cellphone,
You can place and receive calls from your home phone as your cell
so I place the cellphone by the window where it has service and use the home phone to dial and receive calls, It even alerts you when you have a new SMS.
the one I bought you can connect 2 cellphones at the same time and it works great,
Another thing we gained when my wife comes home from work she never remembers to turn off the vibrate mode until then she always missed calls, since then when the cellphone is home it will ring on the home phone.