AirPrint, a long awaited feature brought to iPhone and iPad users via the iOS 4.2.1 update, has so far proved to be somewhat limited, as only a handful of printers – all built by HP – are compatible. HP seems to be strongly backing the technology, as the company is adding AirPrint support to more and more of its printers. Earlier today, the printer maker released firmware updates for six additional printer models, pushing the list of its AirPrint-compatible printers to eighteen. The newly supported models are exclusively “all-in-one” models, namely the Officejet Pro series (8500A, 8500A Plus, and 8500A Premium), the Officejet 7500A Wide Format, the Officejet 6500A, and the Officejet 6500A Plus. AirPrint, an iOS-specific feature that allows users to print documents directly from their iOS-powered devices, was heavily marketed by Apple prior to the release of iOS 4.2. iPhone and iPad users were supposed to be able to wirelessly print to any printer shared by PCs and Macs on the same network, however, the feature was crippled at the last minute, and limited to AirPrint-compatible printers only, due to patent-related issues. As a result, the list of compatible devices was severely reduced.