Have you tried to type in APN and dail number manually? http://www.tp-link.com/en/faq-400.html

As i know, this problem has been fixed already since firmware 140912... You can read notes. http://www.tp-link.com/en/download/TL-MR3420_V2.html#Firmware You may try WAN only mode or connect WAN...

Your model is WPA2220KIT? As the Wi-Fi light is not on, press the Wi-Fi/Wi-Fi Clone Button for 5 seconds to enable the wireless function and check if it will be flashing or not.

If you cannot find it anywhere, maybe it isn't for sale separately...

Did you try to configure DNS server on Android devices instead of router page?

No such a feature...