WiFi-to-WiFi hotspot is a good idea, I don't think all phones can do that though. I once used my rooted Android to spoof my Wifes MAC address to use her in-flight WiFi she paid for after she was not using it anymore.
Even the venerable (and ancient) WRT54G could do this with appropriate firmware.
IIRC, I've even used this functionality with Windows ICS on my laptop many moons ago
It's not necessarily an efficient function, but efficiency isn't always the most important thing.
(These days, I often travel with a Mikrotik device that I've set up to be a hotspot abuser, so as to provide myself and whoever is with me a slice of Internet while having the immediate appearance of being a solitary device. It does this trick very well indeed.)