First for all, calling TextMe/ FreeTone friends is free and doesn't require any Text Me credit.
And you can also call landlines and cell phones with TextMe Apps, your friend doesn't have to be on TextMe. Depending on destinations, calling is free or requires TextMe credits.
Receiving calls on your TextMe number is always free, and doesn't require TextMe credit.
For more details on how to earn credits, please check the "How to get credits?" topic.
Please check "Where can I text and call ? " topic for a list of Countries.