Have you tried to set APN and dail number manually on web interface of MR3420? If it won't work, you are suggested to report the problem here. http://ticket.tp-link.com/index.php?/Tickets/Submit

It is important to check WAN IP address on its web interface. How did you check or change DHCP settings on its web interface? It is not a necessary step.

To find out the firmware version, you may have to reset it to factory defaults first. Waiting for the screenshot... :D

Can you still find the Wi-Fi name on the phone? Reset the router to factory defaults and have a try.

Remember to update progress of this issue if possible. :) Appreciate it.

You are suggested to consult differences between V1 and V2 here. http://ticket.tp-link.com/index.php?/Tickets/Submit