"Microsoft has stated that its Windows Phone 7 marketplace will reject any apps that use the GPL (GNU General Public License) and similar licenses.
“The Windows Phone Marketplace supports several open source licenses, including BSD, MIT, Apache Software License 2.0, MS-PL and other similar permissive licenses. We revise our Application Provider Agreement from time to time based on customer and developer feedback, and we are exploring the possibility of modifying it to accommodate additional open source-based applications in upcoming revisions.”
For more information on the differences between the BSD License and the GPL, read this post.
Differences between the BSD/FreeBSD Copyrights and the GNU Public License (GPL)