One of the frustrations of developing for Windows Phone 7 is that, without a device in hand, it is hard to understand what the phone actually looks like. It is useful to be able to see how Microsoft implements the built in applications in order to borrow ideas for hubs, transitions, and general look-and-feel.
Enterprising developers quickly built an “unlocked” version of the July emulator image that allows developers to see more of the features and design of the phone in their emulator software.
You should not use the unlocked ROM image for development, however. One problem that has come up concerns making https service calls from an application running in the unlocked image.
If you try to call an https service from the unlocked ROM, you are likely to receive a variation on the Page Not Found error. To verify that this is a problem with the ROM image and not with your code, open up Internet Explorer and try to navigate to a site such as https://careers.microsoft.com/ . If you receive an error, then the issues are likely not with your code but with the emulator image you are using. Switch back to using the official developer image that is installed with the Windows Phone developer tools beta and your web service issues should go away.