I think that how country like Japan do that generally. (They hardly have any services that featuring "grandfathering") and new contract and terms under the new

I think that how country like Japan do that generally. (They hardly have any services that featuring "grandfathering") and new contract and terms under the new plan would be established in the renewal window. But in the US, I believe post-paid plans (as opposed to prepaid) there seem to be fairly major red tapes on changing terms while staying compliant with whatever rules set by FTC and also States' equivalent, and that probably makes this very tricky.