Read the fine print:
The Free International Data is 2G speed. If you are lucky you might be able to read emails, but you won't be able to use a web browser since the speed is so slow. On the other hand, if you are in a country that does not have 2G service you will get 3G service, which is actually usable.
The 20 cents a minute is a good deal, unless you are planning on making more than $10 or so in calls from that country. In that case you might be better off getting a SIM card or a cheap used prepaid phone. If you are going to be out of the US for more than a month at a time, this plan is not for you. See restrictions below and in the link below.
In some countries such as the UK the GSM Sim Cards are free for some carriers, but there is still a minimum that you have to add to the card.
If you are going to have WIFI access don't bother with this and just use google voice to make and receive free phone calls. I use the Talkatone app for Android.
Limitations and restrictions of the T-Mobile plan
There are a few important conditions in order to take advantage of this plan that you need to be aware of:
You cannot be continuously outside of the U.S. for more than 35 days before your plan will be subject to review or cancellation;
Your overseas data usage should not be greater than your average usage within the United States for any billing period;
The plan is only for post-paid customers; no prepaid service is allowed;
Covered countries are subject to change at T-Mobile’s discretion;
Additional taxes may be imposed in certain countries;
T-Mobile Wifi calling is not available with i Phones;
Tethering is not permitted;
The plan is not for extended international use and primary usage must occur within the United States;
Your phone must be registered in the U.S. prior to foreign usage;
Your service can be terminated or restricted for excessive foreign roaming, or for misuse;
See this Article for a very good hands review of the service in foreign countrieshttp://www.forbes.com/sites/marcwebertobias/2013/12/30/why-t-mobiles-new-global-roaming-plan-is-an-industry-game-changer/