iPhone 4 is 326 pixels, I don't think it worths a trade off 3.5 326 pixels for 3.7 with 300 pixels
I think your eyes would be hard pressed to see the difference.
The Atrix is set to 240ppi by default, but can be switched to 275ppi.
It's not at 275 by default due to an issue with the way the dialer keypad is rendered in Android. Hopefully that gets fixed soon.
I can tell you this, at 275ppi, I can't see any difference between that and my wife's iPhone 4 screen.
Atrix 960x540 @275 ppi 16:9 aspect
iPhone 4 960x640 @320 ppi 3:2 aspect (according to Apple's own specs it's 320 ppi, not 326)
We're talking a difference of 55 ppi.
So if Apple had to drop the res down to 300 ppi, I seriously doubt anyone would notice the 20 missing pixels.