O2, the iPhone’s carrier in the UK, has announced improved tariffs for iPhone users, offering more voice minutes and text messages. iPhone users on the most affordable (£35) plan will see their minutes jump from 200 to 600 a month, and their SMS limit go from 200 to 500 messages a month. Users signed up for the £45 plan will now get the same allowances as the old £55 plan: 1200 minutes (up from 600) and 500 text messages. Finally, iPhone…