I am not sure if you can do this via the mobile browser. However like the comment from Ajay states you would be able to do this via J2ME(Java devices), Android and iPhone by actually programming a small interface.
You would need to create some sort of web service hosted on www.example.com. This web service will take a XML message and insert it into the MySQL database. Essentially your application would be run by a user they would press a upload button and this would read the contacts database convert it to a SOAP/XML message and post the message to the webservice.
I suspect the reason you wont be able to do this straight from a browser would be the fact that if a browser got hijacked/hacked/infected with malware/virus it could upload your address book without your authorization. Most mobiles are strict with the access to the contacts and other phone functions and it is highly unlikely that you would be able to get around this.