Open Your WP7 project and look into Debug menu. You will see disabled (probably not) menu item Start Windows Phone Performance Analysis
To enable this item You have to switch Your project target from Windows Phone 7.0 to 7.1 in Project -> Properties menu. So if Your application targeted current market, you have to make project clone prior profiling, cause You cannot switch back to 7.0.
When application targeted Mango You can open profiler. Choose options and click hyperlink Launch Application.
After working with application click Stop Profiling. After analysis You will see profiling results. Select timeline and it shows details.
Update: Finally found MSDN Page, describing WP7 Profiler