You can decrease the framerate, which you might do to conserve resources, but the framerate cannot exceed 30 frames per second on the phone.
The line I am referring to is:
TargetElapsedTime = TimeSpan.FromTicks(333333);
Although the emulator will speed up, the phone will not, yet another reason to have a phone to test with.
Seriously, to mess around with this is more advanced, and only do it when you are early in a project, not late in a project.
When I tested this it just messed with my brain, but it was kind of interesting. No problem to generate a little code to test this, I used my bouncing ball example and just changed the number up and down and watched what happened. This is in a previous blog entry: