People have been asking for this for a while and Marvel have been promising it. It went to beta in December but now it's all proper and everything. Marvel Digital Comics Unlimited, or now the less DC Comics-baiting Marvel Unlimited is a fully fledged iOS App, delivering all-you-can-eat streaming of past Marvel comics to subscribers. According to Gizmodo, an Android App will follow soon, though it can also be accessed through the browser.
The price is the same, $10 a month or $60 a year, and the App is accessible to existing customers.