Understanding how SMS messages work is the first big clue that it isn't cause my a faulty location script in the phone itself..
SMS and voice DOES NOT GO THROUGH EVDO.. it goes through teh 1xRTT signal that your phone is always in (unless you have no signal at all).. SMS is really a data notification hack that the cell companys exploited to allow short messages (this ist he reason sms are limited to 180 chars)... These are routed through the cell tower, then through the routers and main database (it can also be forwarded at this point to the other carrier database for processing) and sent back out through another cell tower, through the data stream notification (all over the voice carrier stream mind you) and to the persons wireless device (this is why you can recieve texts while on voice calls but cant recieve other data while on a CDMA network)...
This has no relationship to where your phone "thinks" it is, since these are tracked through the router and main database at sprint.. If it goes through a US cell tower, and out a US cell tower, it knows it was a US based text, If it goes in through a US cell tower, and out a non-US cell tower.. they know it is an international text.. Once again.. SMS go through the VOICE STREAM NOT THE DATA STREAM this is why you get charged for it, if it went over the data stream (like all other programs do such as e-mail, Instant messaging and others) there would be no surcharge for international or limitations on the AMOUNT of texts you can send.. there would be bandwidth caps (like there are for data) on how much bandwidth you can utilize...
Yesterday when I was purposely draining the battery, I started everything I
could think of that tool juice. Towards the end I went to check Google maps and My location was somewhere in Asia (could not read the Asian characters and the names of the small towns did not ring a bell as to where this was). As soon as the battery was set to charge (using the wall charger) My location again was correct (at my house in Boulder). So perhaps that is what is going on? Your battery is low and GPS gets confused, you send a text msg and Sprint thinks you are in some other country...
This is because more then likely the GPS (along with wifi and other stuff) automatically kicks off once you get below the 15% battery meter level (even if you battery is still half full).. It defaulted back to the broken wireless network location script (you have both of them checked i assume.. Use wireless network and GPS).. Also note the Moment implements location via avalible WIFI signals in your location and either they have coordinates, or skyhook (or another service) has those coordinates and determines were you are based on that... Once again.. these services kick off below the 15% battery mark to "conserve power"...
As someone else has already stated.. the reason you are getting charged international text messages is because some sloppy dev is sending SMS from your phone to an international number...