hm I'd do it the easy way (I do this now)
I just have phone always have wifi on (even during sleep) so calls can always be picked up
then using google voice to make/receive calls via wifi on the phone. This isn't exactly a landline but it works like one
about turning landline into bluetooth, something like this might work for you
http://www.amazon.com/Cobra-PhoneLyn.../dp/B0043D2IBE