I hate the fact that you're limited to Apple's presets. I'm in Brazil, but I hate the fact that I can't choose wether I want a 12 or 24 hour clock and I especially don't like the calendar week starting on monday. So I switched to the "united states" preset. The week now starts on sunday, and I now have a 12-hour clock, but the phone number formats are completely messed up. I googled this and found no solution, so it'd be awesome if there was a tweak to customize these formats.