Microsoft has announced the http://www.bing.com/community/site_blogs/b/maps/archive/2011/05/05/new-bing-maps-ios-sdk.aspx that provides the developers with a set of Objective C classes to develop iPhone ans iPad applications withing xCode .
You can signup fot the Bing Maps Key for free here
You can download the SDK here
The SDK is supported on the following Operating Systems – Apple Mac OS X , Mac OS X Snow Leopard, version 10.6.4 or later on a Macintosh computer with an Intel x86 processor , Xcode version 4.0 or later ,the latest version of the iOS SDK.
The Bing Map SDK allows the developers to add Bing maps to your native iOS apps . The SDK also includes the documentation ans several sample projects to help the developers get started .
“With a rich, gesture-based UI provided by Seadragon, the Bing Maps iOS Control provides support for adding pushpins and other overlays to the map, allows your device location to be displayed, and provides the ability to retrieve contextual information for a given map location”
Download the SDK here