Amazing idea, but then the rest of the world (non-americans) are still worried about the implications of this for PRISM. Getting the rest of the world online is cool, but then the NSA gets to have access to their data,that's not cool and I was beginning to like Google!
Yes it will be possible to have a user with a feature phone to auto check-in but that will be from an application level. My company http://www.saya.im has a chat application tailored to feature phone and one of the features is a geo-location chatroom. We are able to do this using cell-tower id's and triangulations and augment that with the phones IP address. There are open-source cell-tower id databases like http://www.opencellid.org/ which can be of help. Also you may want to think of a Java ME app to implement this.
So I'm wondering, If humans can create things that did not exist (computers, mobile phones, cars) etc, to solve problems they had, will it be too far fetched to assume that we were also created by someone/something more intelligent to do something?