While a typical customer for any of the four major carriers in the U.S might think all Samsung Galaxy S III are identical, their processing speeds differ by a noticeable margin. A CNET representative did several tests on a GS3 phone, which took more than a month to complete, to find out which of the four major carriers in the U.S. had the fastest and most constant speeds. There are many factors that affect data speeds including how well a carrier can cover a whole neighbourhood, infrastructures, that could interfere with the signal, and concentration of users of the network at any given time. Therefore there is bound to be some differences in speeds and it is rather difficult to find the fastest among them. There is also the issue of diagnostic speed results against real-world test. The representative used download speeds as the standard real-world test.
The results she obtained might be different from those that would be received by people who are in different locations, and the outcome might also vary due to several other factors that were not accounted for by the researcher. Carriers frequently try to build up and upgrade their networks throughout their market, which means that the data transfer speeds are spontaneous and not constant. She recorded speeds for AT&T, T-Mobile, Sprint and Verizon, while she was in San Francisco. AT&T had the fastest peak diagnostic download time, and it was also the most consistent in speed differences. Verizon had the highest and most consistent diagnostic upload speeds. T-mobile had the fastest real-world times for web loading and game downloading. However, Sprint was the only one left legging behind.
AT&T is so far the winner of the data speed tests that were carried out by the CNET representative; to be more accurate that is only true in San Francisco. This conclusion was drawn because it had the highest peaks and it was consistent in the real-world file transfer test; Verizon and T-Mobile are tied together for second, because T-Mobile has faster download speeds. Sprint will be the last of the pack, and until things change it is the slowest network in San Francisco.