Not just open source
The Microsoft Windows® Phone Marketplace Application Provider Agreement actually applies not just to open-source applications, but any applications which can be redistributed without charge - be they open source or proprietary binaries. So if you want to allow your users to, e.g. share that application directly with others without recompense, then you can't put on the marketplace. The relevant sections would seem to be 1.l.(iii) and 5.e listed below [esp. note the use of the word 'or' in 1.l.(iii)]
Terms and Conditions
l. “Excluded License” means any license requiring, as a condition of use, modification and/or distribution of the software subject to the license, that the software or other software combined and/or distributed with it be (i) disclosed or distributed in source code form; (ii) licensed for the purpose of making derivative works; or (iii) redistributable at no charge. Excluded Licenses include, but are not limited to the GPLv3 Licenses. For the purpose of this definition, “GPLv3 Licenses” means the GNU General Public License version 3, the GNU Affero General Public License version 3, the GNU Lesser General Public License version 3, and any equivalents to the foregoing.
5. Application Requirements.
Each Application you submit to Microsoft for distribution through the Windows Phone Marketplace must comply with the following requirements (the “Application Requirements”):
e. The Application must not include software, documentation, or other materials that, in whole or in part, are governed by or subject to an Excluded License, or that would otherwise cause the Application to be subject to the terms of an Excluded License.