I agree with the sentiment of your post, but regarding this:
said by anon anon :Verizon will eventually re-farm their 2G and 3G spectrum and so will at&t. That is several years away. No only because it takes time but because also the small % of luddites will bitch to the nearest congressperson if these companies try to makes their 2G flip phones non functional.
Keep in mind that phones are not the only devices using the old networks. OnStar, wireless security systems, tracking bracelets for criminals/defendants, time servers, etc. All of these devices will have to be upgraded before the old networks can be completely shut down.