New 2 year contract required for any plan changes ? is this new ?

I just called to reduce my plan from unlimited to something else because my wife's full time job means she doesn't use cell so much.   T-Mo said any plan change requires a new 2 year contract.   I am pretty sure I changed plans in the past without having to extend conract for 2 years. 

They said if I had 1000 minute plan and wanted to change it to 1500 for example . new contract required.  This doesn't even make sense (to me)

Is this new ?   Is this the way Verizon and ATT work ?

They started this back in the summer when they grandfathered all of their plans and went exclusively with the Value and Classic plans.

I'm not sure how Verizon works.  I'm relatively certain AT&T does the same thing.

It extends the contract end date always. But it does not make you wait longer to upgrade on Classic.