This new feature goes live from Oct 20 for new customers and Oct 31 for existing customers. If someone could report back the data speed while using their smartphone out of the US, it would be appreciated.
I have stopped by T-Mobile store and have called to get an authoritative answer on this question.
I am a very long time T-Mobile customer (since the old days of VoiceStream) and was a bit worried about that Oct 31st date because I am going to Taiwan this week.
Both at the store and the customer support on the phone said it is Oct 20.
I still will be cautious and will do a simple test of sending one text before I turn on data.
The following web page does mention Oct 20th without restriction for existing customer, though other pages do mention Oct 31st still.
PS: The page I linked to now says Oct 20 for new customers and Oct 31 for existing ones. So I am thoroughly confused.