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.
W3C defined Contacts API as a working draft but as far as I tested it's not supported in iOS devices(I have iPad with iOS4 and iPhone with iOS 5). You should test some android devices and tell us if they support Contacts API or not. That would be useful for future readers.
In case you have contacts api supported you can do this:
if(navigator.contacts){
var mycontacts = [];
navigator.contacts( ['emails.value', 'name', 'friends'],
function(contacts) {
for(i in contacts) {
mycontacts.push(contacts[i]);
} );
}
The first Idea i got was to use for Android (most Android-User, have a Google-Account) the Google-Contact-API.
I'm was searching for this too, and I found only this "near" solution:
a video here: http://www.youtube.com/watch?v=e-2D3uCV2bE
Personally I found that solution a bit buggy, this is safer:
a video here
http://www.youtube.com/watch?v=Ws99exsZEIs
CONS:
it's counter intuitive
you need android and QR droid installed
I don't know if it's possible with iphone, and other mobiles.