Apple's (NASDAQ:AAPL) iOS 4.3, which will be available for download March 11 for the iPad and HSPA-based iPhones, will add a personal hotspot feature for iPhone 4 users on AT&T Mobility's (NYSE:T) network. As expected, AT&T will charge subscribers $20 per month to use the feature. AT&T customers must subscribe to the $25 data plan that gives them 2GB per month, plus the extra $20 tethering charge that gives them an extra 2GB of data. In total, subscribers will pay $45 per month for 4GB of data plus hotspot sharing when the feature arrives in iOS 4.3. Verizon Wireless' (NYSE:VZ) iPhone 4 came to market last month with built-in mobile hotspot service for an additional $20 per month on top of the operator's $30 per-month data charge for iPhone users. Article