It's not T-mobile. it's actually the type of phone your friends/families have.

A friend of mine had BB storm on Verizon. Whenever she send me an image, it would look quite small even after saving the image. I got her Moto Droid and now the picture she send me are very big. (Cover N900 screen if saved) In FmmS, it would take up about 66% of the screen or more.

Same experience with Google G1 - good image while Samsung something.. small image.

From what I learn from this thread, 300 is the setting you are senting out to people. So far, I changed my setting to 600 and it work perfectly fine. I will probably try 1000 until I sent out the same width as my friend Driod.