Windows Phone 7 is a big shift from Windows Mobile 6.5 and below, especially from the enterprise perspective. A lot of companies in the past have custom-developed apps in C++ and other languages that run directly on the phone. With Windows Phone 7, that's no longer possible. Every application must be developed using Silverlight and/or XNA Studio, and deployed to the device through a Microsoft provisioning process. There have been hints that it may be possible in the future to deploy applications directly to the device for enterprise purposes.
That being said, if you can get by with those stipulations, you CAN read bar codes from the Windows Phone 7 by using the built-in camera. At the MIX '10 conference this year, they demoed a Silverlight eBay Quick Lister application that recognized bar codes using a web cam. You could write an application that does the same using the phone's camera.