Dialer one, maybe AOSP dialer?
I, however, don't agree at all that it is slow though. I'm not quite sure what you have done, but once I click "phone" the dialer is up by the time I remove my finger. Its blazing fast. As for lookup, as others have stated, I just hit phone, type "Mike" for example through T9 and there he is, instantly. You want slow, you run the phone app on the Hero. lol
And I don't mean to bash what your trying to say, all I'm saying is if you consider it to be slow, something else might be wrong..
Now if your talking about the phonebook, that is a different story. The sense phonebook does have the alphabet on the right, as you describe, and is a little slower to load depending on how many contacts you have. Why use a phonebook though when you can pull up the dialer and simply type a name