i am an avid user of T9 predictive text messaging. i find the concept simply fabulous. some days back i was thinking about it, when i concluded some things about it. essentially, T9 is a function with one to many mapping, with an added condition such that for every element in the domain, the corresponding element or elements in the range are arranged in a fixed order. and this order is preset worldwide, based on analysis of frequency of usage of words in messages.
one thing that we can control while designing a system like T9 is the order in which different words with same combination appear for that key combination presses, but something we cannot change (fundamentally) is the unique key combination for a word (the key combinations are elements of domain set, while words are elements of range set). and it is because of this limitation (and by sheer coincidence too) that there are certain key combinations which result in mutually-conflicting words, and here lies the potential for problem.
what happened with me was that i got a message "what did you do about sony ericsson k750i?". what my friend was asking was whether i selected the phone or i rejected it (i was in the process of finding a suitable new phone for purchase). since i was in a hurry that time, i quickly hit the reply button and pressed keys in this order 7--> 3 --> 5 --> 3 --> 2 --> 8--> 3 --> 3. the word by default that comes for this combination is 'selected'. in reality i intended to write 'rejected', which, incidentally (and unfortunately) has same key combination as 'selected'. i had almost hit the send button when my finger spontaneously went numb (maybe my reaction time has lowered down) and the message did not get sent. i pressed the 'next word' key and then sent it. considering the situation, its certainly not a big deal even if i had sent 'selected' instead of 'rejected', since neither it mattered, nor it was non-amendable. yet it surprised me so much that here i am writing a blog about it. and i almost murmured to myself "oh my! what a coincidence!".
i believe such 'delicate' key combinations need to be found out by brute force coupled with dictionary lookup of valid words (so as to reject invalid words coming out of brute force) (with included logic to group words with similar key combination) and coupled with manual inspection to detect potential conflicts. conversly, a dictionary with all valid words coupled with a valid-word-to-T9-key-combination mapping program (again, with included logic to group words with similar key combination) and coupled with manual inspection too can serve this purpose. and for whichever key combinations there is potential of troublesome meaning, when a user forgets to change word for a key combination, there the phone should highlight the potentially-troublesome word(s) on the display as a reminder to user to have a re-look and make sure he has chosen the right word(s).
i really believe this should be done. not a necessity, but certainly a nice addition, and sometimes helpful too. especially when my beloved T9 can covert a casual sounding "hey i heard you have got many movies" to an inflammatory "hey i heard you have got many mother". creativity with such combinations has no end ;-)