Urban Airship, a startup that makes it easier for mobile app developers to offer push notifications, in-app purchases, and other key features, has closed a new $5.4 million funding round. The Series B round is being led by Foundry Group, with existing investors True Ventures and Founders Co-op also participating. Foundry Group’s Managing Director Jason Mendelson will be joining Urban Airship’s board.

The most recent addition to Urban Airship’s feature-set is support for subscriptions, which are sure to play an important role for publishers in the coming years. The startup powers the subscriptions seen on the recently-released Newsweek iPad application, which is the the first iPad periodical to feature them (don’t be surprised if more publishers turn to the startup to power their subscriptions).
Other clients include Tapulous, LivingSocial, and Gowalla. Urban Airship previously closed a $1.1 million funding round in February, so this brings their total funding to $6.5 million.