Since I'm one of the folks who strive to compose complete and grammatical SMS messages, I use T9 quite a lot. Because of that, I've "discovered" something I call "anT9ms", that is, a class of key combinations which produce words which are opposites of each other. I don't have a long list as yet, but here's some that I found:
735328 - REJECT / SELECT
735328466 - REJECTION / SELECTION
7874 - RUNS / STOP
7873 - SURE / RUSE
Found any more? Let me know!