How to Block Calls on a Windows Phone 7
So how does a user utilize WP7 call blocking? Well that can depend on the carrier, the app, and a directory service.
Which Carriers Block Calls Windows Phone 7?
Some landline and cell phone carriers have features that will allow a user to block certain calls, however, some don't. For instance, AT&T has a feature (with some phones) that will block calls, however, it only reroutes calls to your voice mail and doesn't really 'block' the caller as one would expect. Sprint, on the other hand, does not have a feature on any of its phones that allows for call blocking.
Call blocking can usually be set up via either the phone or a third party app. Currently, Windows Phone 7 does not have the ability to block unwanted phone numbers.
Customers of both AT&T and Verizon are able to block unwanted callers, while Sprint and T-Mobile still do not have any available feature to provide this.
Another avenue is that of third party apps, unfortunately, as Windows Phone 7 is still relatively new, call blocking apps are not available for the phone as of yet.