Eventually, I have no idea about that.
As for C#, I only have some experiences about network services on Windows Mobile/CE but not Windows Phone 7.
I try to google about “Windows Phone 7 & C++”, and I found if you are the OEM of Microsoft then the answer is yes, otherwise you can’t do this.
Maybe what we can do is just waiting Microsoft release something like NDK.
Sorry, there is no useful message here.