T-Mobile cell equivalent to iPod+Phone?

Hi. I am a low end user of cell phones, but would like to get a new phone that will let me do WiFi as well as pre-paid calls. Is the LG Optimus T the right phone for that?
I'm told that the APPS on it won't work without a data plan, but why not? The Apps all work on an iPod or iPad without a data plan, simply through WiFi.

Would appreciate any advice here.
I don't want to spring for $544 for the new Nexus S of course.

Arroway