The best size I have used is 240x440 it fills up the whole screen without any distortion or close to none. I just use Photobucket to resize the pictures I want to use and than either text/email it to the phone or send to my microsd card and load it up. If you want to text/email it from your computer you just need to use your phone number
1234567890@vzwpix.com and it will come over as a text message and you can save it to your pictures from there.