I use a Dock N Talk.
http://www.phonelabs.com/prd05.asp
There are others out there, but I've had this one for over 4 years. This one only allows one bt phone at a time. Some newer/other manufacturers allow 4. Pretty cool.
I have no landline. It's a device that you plug into your wired house phone lines. I then plug one house phone into that. Then any phone in the house that is wired will essentially be an extension of one's cell. Works well for me. And yes, it does reach to some of my garage so I have to get our of range to connect to my MDX. Sometimes it does it automatically others, I have to force it. Who knows why? That master/slave may be the issue- along with where the range of the house BT really is. In the garage, it has been spotty, but since I don't leave my cell in the garage, I've never delineated it.
When I return home and shut off the MDX, the phone reconnects to the house. It should be a bit fun with the EX. I'll play around with it and see what happens.
Thanks for your contributions on the board!