It is improtant to confirm that IP address obtained under 3G/4G is a public one. If not, you should contact your ISP to solve it. private IP range:10.0.0.0—10.255.255.255； 172.16.0.0—172.31.255.255；...

To upgrade the firmware, you have to connect PC and PA4010, and then run the utility on the PC to upgrade it. How did you upgrade when it is connected to your router? :confused: Anyway, maybe it is...

How did you install the driver? http://www.tp-link.com/en/faq-228.html It should work...Anyway, it seems that you have given up...lol

I've tested without the Range Extender... web pages are slow to load as the videos. Maybe you should contact your ISP to improve your internet speed. As I said, RE can help to improve Wi-Fi signal...

There is update with new firmware and you have to change some settings. http://forum.tp-link.com/showthread.php?80773-Setup-Simple-PPTP-VPN-server-and-TL-ER604W&p=160068&viewfull=1#post160068

I'm not familiar with Ubuntu. On Windows PC, we can find such an option. You have to configure multi-nets NAT entries as well.