As spotted byThe Mobile Report, the change went into effect on Jan. 18.

So what exactly is going on?

Here is what you better know.

Will T-Mobile be throttling speeds for heavy data users?

The carrier says it will notify users when they pass this 1.2TB threshold.

Read more:Our T-Mobile Home Internet review

Can I buy more high-speed data?

Why is T-Mobile doing this?

What is data pipe prioritization?