Like I said on my previous post, the device MUST support it, for example, if I ran that code on my EVO I can see and get the WiFi Tether Settings and activate them, if I ran the same code on a Nexus 7 tab, I open the screen but the screen is BLANK, on a Galaxy tab shows the settings and able to change the settings, on other devices you might even see a blank screen like I mentioned or just disabled buttons.
Like Erel also mentioned, it's a hidden API which is usually managed by the telcom provider.