I think Franko's recommendation, Coffee Cup RSD, applies a mobile first approach (am still waiting to evaluate it myself).
Anyway, as I have said elsewhere I have no problem in the short term to 'waste my time' on building two separate versions using NOF. It doesn't take that long.
I've just published a website for
www.lookinggood-aberdare.co.uk - this is obviously the desktop version.
The code automatically routes to the smartphone version BUT you can view the smartphone version on the desktop using:
www.lookinggood-aberdare.co.uk/m.lookinggood
It has a different menu on the mobile version as well as a 'click to call' button that would be mostly pointless on the desktop version.
The Reviews are also different because scraping from Facebook Reviews (not easy) I could not enlarge it to show correctly on the mobile version.
In most replacement software I've tried so far I would have had to alter things like font etc so am I any worse of building a NOF mobile version?
Typically my clients don't change their sites too much apart from one of two boutiques.