Urban Airship, mobile app optimization engine, has closed a Series B funding round, totaling $5.4 million, led by Foundry Group.  That brings the total amount invested in Urban Airship to $6.5 million.  This latest round of funding will be put towards the company’s ongoing growth.

As part of the deal, Foundry Group Managing Director Jason Mendelson will be joining Urban Airship’s board of directors.  Existing investors True Ventures and Founders Co-op participated in this round as well.

Urban Airship is a tool that powers things like push notifications and other alert systems, as an add-on for mobile apps.  The tools from Urban Airship are designed to enhance existing mobile apps, making them better able to interact efficiently with consumers.  For the mobile space, this means direct interactions, which is also where Urban Airship’s potential around metrics comes into play.

“Urban Airship really impressed us with its foresight into the mobile market. The team there knows the market better than anyone else and is consistently out in front of what customers want and need,” says Mendelson.

“Urban Airship’s early traction of securing more than 4 thousand customers sending millions of messages every day and reaching 45 million devices is extremely impressive.”

This early hold on a mobile consumer audience is also showing gains with in-app purchases, as optimization around their delivery tactics will lead to more effective targeting and delivery.  Overall, in-app interactions is a major frontier for mobile applications, and it’s also something that will operate independently, between apps and mobile websites.

These are areas Urban Airship will surely foster, as this allows the service to offer a great deal of metadata back to its clients, the app developers themselves.  Urban Airship’s “secret sauce” is in their cross-platform delivery methods and support, CEO Scott Kveton tells me in an interview last week.  It’s a centralizing mechanism that enables the developer to support iPhones, Androids and more, with the “proliferation of the different platforms” acting as an important strategy for Urban Airship.