Even though cellular south is behind in the android OS versions, the rom they have running on the phone is a lot faster than any of the other companies. Everyone gets the same phone from samsung and they tailor the OS to their needs before they flash it to the phones that go to the stores. Most companies like verizon, t-mobile, and att will make a few changes and have the phone out as fast as possible while sending periodic updates through the air.
Well, since cellular south had a lot more time with the phone before they released it, they had a much larger list of issues they found with the phone, as well as being able to see the issues that the larger companies had. This means that the rom that cellular south flashes to their phone is a lot faster and runs more efficient than the other companies do. I know this for a fact because I have the galaxy s through them and my gf has it through tmobile. We got them at the same time yet when we hold them side by side, mine runs faster, opens apps quicker, and has a longer battery life even though we both use them throughout the day.
Also, if you root (jailbreak) your phone, you wont be able to receive the updates they push out to the phones. This is a problem for the companies that try to rush the phones out to get the competitive advantage and only fix major problems after the fact through updates. With cellular south, they fixed over twice as many issues as any other companies before it was released so you would be safe rooting your phone and knowing that it doesn't have many updates that you would miss.
I can also say that since I have rooted my phone, I have downloaded apps that scale down your cpu when you dont need much power and scales it up when needed. You can make your phone run faster all the while using less battery power overall.
If i were looking at comparing the Iphone4 to a galaxy s from cellular south, i would go with the samsung. If I were comparing it to the galaxy s on the other carriers, I would choose the Iphone4.
Sorry for the long post.
