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> You have these problems with carriers as well. They're technically interoperable but they hit you with prohibitively expensive rates if you try to do anything international.

And very poor transparency on those short codes... I once got some extra charges, because of a shortcode (it was actually Yahoo!) I happened use was international. (No way to tell that by the number alone.) It was surprising to hear from the carrier I didn't have any way to block international text, too.