For me, and I don't think I am unusual in the US at least, texts to anywhere outside of the US, Canada, and Mexico aren't allowed without paying extra. Texts to many countries aren't allowed at any price.
I can text literally any phone number, given I have enough money booked on the account. SMS is by nature not centralized, the data is exchanged between mobile providers.
If you were to start your own mobile provider, you could text anyone everywhere given you manage to get peering.
For me, and I don't think I am unusual in the US at least, texts to anywhere outside of the US, Canada, and Mexico aren't allowed without paying extra. Texts to many countries aren't allowed at any price.