The XLink BT allows you to make and receive calls from your usual land-line phone over your mobile network. Once set-up you simply need to leave your cell phone within Bluetooth range of the XLink box and then any calls to your cell will ring and be answerable around the house and calls made from your regular phone will be redirected over your cell.
One of the advantages of the XLink is it allows you to ditch your land-line and make the most of the free calls that you get with most cellphone contracts. It can be used with 3 cellphones simultaneously, with each cell generating a different ring tone on the other phones (when calling out you specify which cell to use by a numeric prefix).
XLink retails for $80 and is available from My XLink though you may want to wait for the next version as that willinclude Skype functionality.