It could be that the carrier has taken steps to avoid the problem. I don't know if these phones can have their software upgraded without the owner noticing or not.

For that matter, it might only be certain versions of the handset software that are vulnerable.

Another possibility is that the carrier could do some sort of filtering in their SMS server software to turn the "dangerous" text into something innocuous, for example by inserting a space into the string somewhere.

Remember what every programmer and QA engineer *should* know: it's impossible to prove the absence of bugs by testing.