Depends on the phone. I hate the predictive text function, but you need to use the options key (different on every blasted phone I have!) to just go to "Ab" (or similar entry) without any "T9" logo (the predictive text junk).
Sorry, without knowing your phone, I've no clue. FWIW, I have Alcatel, Siemens, Motorola, Sony Ericsson and Nokia phones, each seems quite different - some allow you to turn it off from being default, others need you to switch to different (non-T9) mode each time.
(Oh, and yes, maybe I am a bit sad having tried so many phones, I do like to have an radio with me when out walking and these are all with FM built in, so "in touch" if needed and no need to carry separate radio.
NB Some are a few years old, and with numbers different people have stored... at one time I planned to kit out my sisters with Virgin mobiles so we could chat at 3p a text, but they're all older than me and only one bothers with using her mobile... she's stuck with the same number for years and I hoped she'd stop being ripped off by leaving her contract - she doesn't need to use it as much since retiring from being head of a junior school.)