I've been fighting with a WiFi extender in my US home for quite a while now. Sometimes it works great, then for no particular the no signal orange light comes on and it needs to be rebooted. Looking at forums on the subject this is not an uncommon problem. I'm feeling at this point that relocating the router to a more central location and getting a higher end one may be the better option. Duct work and metal seems to be a problem for the wifi signal. As far as the Magic Jack, what we have done in Mexico is locate the base station of a cordless phone system near the router, then just use satellite phones in the rest of the house.
I have this little guy in my condo to convert wired internet into wireless in my unit. But it also works as a repeater- i.e. take a WiFi signal and re-amplify it. It DOES require a laptop to setup but it has a wizard and is pretty easy to setup (less than 5 mins).