I\'m currently building a site where, with one touch, you should be able to add a contact to your IPhone/Android Address book. The website is currently HTML5, but Javascript
You might have to attack this from the device side of things instead. If that's what you end up doing try a cross-platform framework.
Not sure what your flexibility is, but for cross platform device integrated application I highly recommend PhoneGap. Plus, sounds like you've got some experience in HTML5 and CSS already. This could handle your contacts integration pretty easily across devices.