T-Mobile has been offering it for a while. This year it will be offered on T-Mobile Tuesday (and you have so many days to activate it). If you have already signed up for mlb.tv through T-Mobile, then you have to cancel by March 22nd and resubscribe. You can watch from your phone, tablet, or other connected devices (I'm assuming that if your phone and tv support casting, you can watch via the tv). However, "hometown" blackouts apply. You can also use multi-view to see up to four games on one screen at the same time. Or, listen to the radio broadcast from either team.