I helped a non-techy friend buy an iPhone 4S on contract. He has a 500MB/month data allowance. He blasted through it in the first few days, then again within a week of his second data allowance. He uses the iTunes Store app a lot, so I ran some tests. I installed Dataman Pro on my 4S (5.01), and results as follows [data used in square brackets]: Load iTunes app (music/new releases page) --> [1.6MB] Select an album; loads album page --> [~90KB] Listen to 4 different songs for 1-2 seconds ONLY --> [3.1-3.4MB PER SONG!] Go back to the main music/new releases page --> [1.3MB] TOTAL usage for this seemingly simple set of operations equates to an astonishing 16MB!!! This was accomplished in the space of no more than 10 seconds! This test was performed on wifi so it's likely that 3G use will take a certain percentage longer. But let's just say that it took 60 seconds instead of 10 seconds to do the same on 3G - in one hour I would have used 960MB!! ******, that's a lot. Ok, I've just tried the same thing on 3G three times in a row. For the same set of operations (but selecting random albums) Dataman reports ~11MB the first two times, then 7.9MB the third time. I cross checked these figures with Mobile Network Data under Settings --> General --> Usage --> Mobile Usage. First test was 6.7MB, second was 9.6MB and the third was 8MB (note that this was combined upload and download data). The Dataman vs iOS figures are not consistent, but the point remains that browsing the iTunes store consumes a crapload of data. I completed each test in under 20 seconds, so I could easily frizzle away well over 1GB in an hour! FYI my 3G speedtest.net results were 4.01Mbps download before I started the test. My friend upgraded from an iPhone 3G. He had a 3GB monthly cap on that, but he never once hit that, even under relatively heavy usage. He has always liked the iTunes store (until now!). I don't use the iTunes store so don't know if it might have always been like this or not. Go ahead, try this yourself, I'd like to know it's not just me. And I'd also be interested to know if anyone has vastly different results on a different phone or OS version.