Agreeing to terms automaticly

A post I found here shows a video of a site where before you finish entering your details for ringtone downloads, it automatically adds a checkmark next to the "i accept the terms" line. When you try to disable it, it comes right back on, and should you finish entering your number, it makes sure that the "i agree" is set to "on", and clicks the continue button automatically.

I wonder how that company thinks that is legal...?