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Millions of smart meters will fail when 2G and 3G turns off
(www.theregister.com)
This is a most excellent place for technology news and articles.
Not complicated at all. For the most part, all they do is swap one box - the transmitter. That's it.
(However, that doesn't consider other things, like improvements in redundancy and safety, or construction standards that didn't exist back then.)
But really, all that needs to be done is pull out one box, and slide in a new box. Not complicated at all.