They are the mobile specialists that you've been looking for. They can help ideate, design and develop applications and their backends. All of their work revolves around the iPhone, iPad, Android and Node.js
They can help create new products for your team. Most clients prefer to have them churn out the first version of the product while they setup an internal team for development and support.
They can take your existing mobile and web products, and redefine them for your customers. The usual suspects would be products which haven't been worked upon in a long time.
They can help migrate your products to new platforms. Most products start with a smaller set of platforms, due to a lack of time or budget. They help in taking them to newer platforms.