Copy a file to phone folder

I want to reward the user with wallpapers and ringtones. So I think the best way is to copy it to the cellphone’s memory (as I far I know, there’s no function in Unity to set Ringtone/wallpaper).

I can have those files in the game pack, or I can have it on a webserver. How can I copy them to a cellphone folder?

It varies per phone OS, and most have isolated storage, making it difficult. You might find it easier to have the user enter an email address, and have your server automatically email them. Or host the images on a webserver and expose the links so they just save them from their browser.