Hi Rick,
I do not know the details of your T Mobile plan. I can tell you that generally using a mobile phone in another country isn’t cheap because of the roaming charges.
The cheapest way to call these days is via a data based service such as Skype or Rebtel, assuming you own a smartphone. When looking at the T Mobile USA page below I can see that they offer several unlimited data plans for those using the phone abroad.
https://www.t-mobile.com/cell-phone-plans/international-roaming-plans
If you are on one of these plans you could place calls via the Internet by downloading one of the two apps mentioned above at reasonable rates. You can of course connect to a wireless network where available and place calls via the Internet even if you don’t have unlimited data from T Mobile.
One other option would be to get a local SIM card with a local number and use that for local calls. A prepaid service with a “dumb” phone may be a good choice in this case.