The $30 Wi-Fi solution for Nikon D4 described in this post had one limitation - the Wi-Fi bridge did not act as an access point and needed an established Wi-Fi network in order to operate. This setup can be further improved if you use an USB solar battery charger (around $15 on eBay) and the ASUS WL-330N3G mini Wi-Fi router (around $70 on Amazon):
The battery is charged from the sun in about 10 hours or from a PC in 3 hours and can lasts for about 2 hours. The 3G router is excellent, it starts-up in seconds, can share an USB hard disk, can also share its Internet connection via a SIM card, etc. Including a WEB/FTP server in the D4 was a very clever move from Nikon - it gives endless possibilities. I can for example make a script on my Android phone to connect to the FTP server every x seconds and downloads all the new JPEG files (similar to Eye-Fi cards). If the camera is far away from Wi-Fi reach, I can connect to it through the Internet (provided I made a port forwarding for ports 80 and 21 in the 3G router).
Here are some pictures of the setup:
Check also this alternative Wi-Fi solution for Nikon D4.
Thanks to GfK from Patras, Greece for sending in this update.