It looks like T-Mobile is making a change to its plan prices soon. But since existing customers are protected by its Price Lock, the change will affect new customers. 

As reported by The Mobile Report, T-Mobile unveiled a new version of Price lock that will affect new activations and service changes. The change instills that if you maintain a good standing on your account, T-Mobile commits itself to paying your final month’s bill when you decide to change. If the Un-carrier imposes a price increase that will make you want to leave the network, you have 60 days to notify the company of your decision to leave. 

Prior to this announcement, T-Mobile’s Price Lock guarantee was that their customers will not be affected by a price increase as long as you stick with your existing plan.

Customers who sign up to a new line after today, January 18th, you will now be covered by this new Price Lock agreement. If you are an old customer and you make changes to your plan, the new Price Lock version will extend to you. 

Source: The Mobile Report