Unless the amount they have to pay exceeds what it was going to cost them to honor those lifetime agreements this is just the cost of doing business not a penalty
The point of the price guarantee was to get customers to sign up at a profitable rate. Once they stopped becoming profitable they’re fine with you no longer being a customer, they’ll just reel in new ones with introductory pricing or other standard sales pitches.
They sent me a cheque for a penny and insisted I cash it immediately.
(If we want to destroy the banks, just leave a negative balance on your credit - they'll bankrupt themselves in printing and mailing costs... Muwahaha)
With the way I expect to see inflation continue along its current path, I half expect them to argue that their prices are still the same as in year 2XXX prices, adjusted for inflation.
I would be surprised if this goes anywhere meaningful. Those were marketing promises, not contract terms. I noticed the promotion ended just over 2 years before the price hike, indicating that everyone had completed their contract. Once the contract is over, either side can walk away, or renegotiate terms.
Marketing promises ARE a contract. Companies aren't allowed to advertise a thing and then not do that thing. That's false advertising and fraud. Companies aren't allowed to say they offer a product or service for price X and then actually charge price Y. This is well established law.
You either didn't read or didn't understand the article. Multiple times in multiple ways the company said it's offering a lifetime price, which is different than a price offered only for a limited term. They very explicitly said “T-Mobile will never change the price you pay” and "T-Mobile One customers keep their price until THEY decide to change it. T-Mobile will never change the price you pay" etc. etc.
Marketing promises effectively constitute a binding unilateral offer, for the purposes of contract law. When a customer signs up, you also have acceptance, consideration, and intention, thus forming a valid contract. Carlill v Carbolic Smoke Ball Company is the classic case in English contract law; the principles are basically the same in the US.