“T‑Mobile will never change the price you pay for your T‑Mobile ONE plan.” That was the promise. The Un-contract. The whole reason millions of customers picked the magenta team over Verizon and AT&T in the first place. Now T-Mobile is retiring legacy 3G and 4G-era plans — Magenta, ONE, Simple Choice — and automatically moving customers onto “modern” 5G plans at higher monthly costs. Billing changes hit mid-July for the current wave. The company that swore it would never surprise you with a rate hike just sent the notification.
They did, but even beyond that, the other alternatives mentioned in this thread are MVNOs that still use T-Mobile’s network (usually with a lower priority compared to direct customers, not usually an issue unless there’s congestion). You’re still paying T-Mobile, just indirectly. MVNOs buy in bulk and try to offer options that split that bulk usage up in ways different to the big carriers to target smaller more specific demographics.