assuming it supports 5g calling and 5g lasts as long as 3g did it will still function for calls, MMS, SMS, and email at a minimum (assuming encryption doesn't change too much)
In what kind of bizarro world do we live that 8GB of RAM in a phone is not enough? Also 6G is currently expected to be available around 2030, so 5G will most likely still work in 2031.