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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.
How would those microcells be legal? It's not just that 3G or whatever gets shut down, the frequencies are usually reallocated to something else so you can't legally operate a 3G network on those frequencies anymore.
It would depend how regulations are written. It's perfectly conceivable that these can be allowed to operate using a very low power level that wouldn't interfere with the larger network, especially if the use case is for things like substations that are already isolated.