If you want to maximize this phone, you might look into unlocking and debranding your phone.

I know that Rogers (my service provider) prevents me from using Flash themes and from using mp3's as ringtunes, mostly so they can charge me money for something I should be able to do for free. If you're thinking of customizing your phone, look up custom pack software, and even the Sony Ericsson Themes Creator if you want to make your own theme.