Ask HN: What's going to happen to 3G infrastructure as it gets phased out?

I wanted try going back to using an old 3G 'dumb phone' for awhile and in the process I learned that Verizon is going to stop allowing activation of 3G phones on 12/31/2019 and will be 'turning off' their 3G network on 12/31/2020.

I was wondering, what happens to all the old, incompatible infrastructure when a new mobile generation gets rolled out? Do the telecoms lease access to the old equipment? Sell the network wholesale, in-place? Do they liquidate all the equipment to make room for new antennas and equipment? What happens to the unused spectrum once all the providers are phased out?

P.S. I'm bummed out by the lack of truly dumb phones that'll work on 4G (at least, on Verizon's 4G network in the US). The dumbest phones I can find all seem to be android-based. I'm tired of carrying around such a powerful device and wish I could just have access to sms and non-ip-based telephony without it just being a pared down launcher for a general purpose operating system.