Hi rodolfo,
That is a way (I would use m.mywebsite.com ) I see this allot for mobiles sites.
I have seen that Dnn7 also allows you to share modules between portals, I haven't tried this but maybe (a big maybe) you could try and share the nb store module between the mobile site and normal site then see if it will share the data as well.
First (if you are using dnn7) try a test locally it see if this will work.
If not you will have to re-enter all the products/cats etc again for the mobile site.
Geoff