Microsoft has released an article regarding "Windows Phone 7 and Certificates", on December.
This is a great document that you should read as this is a great way to understand "how" certificates work with Windos Phone 7.
As a main point, I would like to let you know that you can use your own certificates, Root CA and Client Certificates.
Windows Phone 7 uses a Smart certificates installer that will automatically recognize the store to be used when you install the certificate.
This certificate installer on Windows Phone 7 supports .cer, .p7b, and .pfx files.
When installing certificates via email, make sure your mail filters do not block .cer files.
You can read the full article at :
To know more about Digital Certificates and SSL, please visit :