You need to clear the Internet architecture, there is no way to web application to access client Info, except Cookies. (If they can, then properly nobody want to access Internet because they can do anything to your harddisk...)
You need to let user trigger something... like select the file in their harddisk and press the "Upload" button, then only you can access to this file...
Like what you said "import" their contacts, also mean "upload" their contacts right? actually they should be the same.... or I misunderstanding your problem?