heya,

first and foremost to each their own,
so this is for the rest of us that want to add custom words conveniently while using the T9, and for those that don't already know.

xT9's quite good actually, better than the asus p525 at least. Well its only good for us t9 users, multitap boys are victims of HTC's logic cycle where xT9 alternates automatically when going from field to field.
i.e. When typing new smses,
in the "to:" field, you get multitap.
when you goto the main text body, you get xT9.

Now back to the subject at hand,
say we want to add the word "salah"...

no need to select the "+" at the end after 1 or more characters have been pressed,
just type 72, which by default gives you "sc", use the dpad and select "sa",

then continue with 5, which now gives you by default, "pal, use the dpad again and select , "sal"

continue till you form the word. i.e. 725, choose,2, choose, 4, and choose.

when you get "salah", choose the centre action button (in the name of convenience)
after this just type 72524, to form salah.

For those of you like me, prefer XT9 always, here's something from the geniuses from another popular website.

a regkey mod is required.

navigate to [HKLM\SOFTWARE\Tegic\eT9\IME]

and add the following dword,

CarrierDefaultTextMode=dword:0
(0 for ABC / 1 for XT9)

Remember to soft-reset properly, (press and hold the power button to shut down, or power off the screen for about 15sec to ensure system writebacks), and watch the wonders :)

btw, it works for the original PIMs, PocketInformant (thanks Gohyc).
So far the only area it doesn't work is in the "To" Field in "new sms". But you can use the tip as mentioned on top to make things convenient.

to make things easier here are two cabs.

*Disclaimer* have tried with the xt9 defaulter.