If you love the mobility and it's checkout, but are married to the template you are using, you can now have the mobility checkout separate!
We have released the best responsive One Page Checkout yet!
http://www.bcsengineering.com/store/smooth-checkout-responsive-one-page-checkout-for-x-cart.html
We've had such great response from our Mobility module and it's checkout that we've created it as a separate module for X-cart! Available currently for 4.6.x and 4.7.x, have the checkout flow you've always wanted!
Carrie