The first change is to their $70 plan with 2GB of data. They will be removing the 2GB to make it unlimited data for $70 a month.
The next change is to their $50 pre-paid plan that at the moment gives you 100MB of data. they will be changing this to allow for throttled speeds so users will not have to refill their account to use data.
While these changes may not be huge they are still better than what was being offered. So if you are looking to get a pre-paid plan with T-Mobile you may want to what in till the 22nd.