Service [Q] T-Mobile MotoX won't Send SMS abroad - gateway setting?

Hi,

I have the US T-Mobile Moto-X. It is unlocked and rooted, running the stock ROM.

I'm abroad in South America and have a SIM and can make and receive calls and use data but when I try to send a text it is stuck on Sending...This happens on new SMS and replies. I have tried two SIMs from different providers.

I'm wondering if there could be maybe a gateway setting or something that needs to be updated.

Any suggestions?

Thanks much!
Mark