how to computing moving velocity of windows phone in street? can use accelerometer?

Before doing that, learn elementary Galilean principle of relativity, http://en.wikipedia.org/wiki/Galilean_transformation[^].
Any mechanical behavior does not depend on which inertial system we observe them in. That said, there is no measurable difference between a phone moving with uniform velocity, no matter what is that velocity.

Well, theoretically speaking (only very theoretically) you can bring the phone is a state of zero speed (relative to what? well, let's say, to the Earth), and press some button to reset a state of your program to a state referred as "zero speed". From that point, start integrating all accelerations to calculate "current speed". In practice, this is just a fantasy. You don't have a real-time system to do that, and even in perfect real-time system, the measurements and calculations are not precise, and the errors tends to accumulate with time. An accelerometer can measure well… acceleration, not speed. And nothing can measure instantaneous speed, even theoretically, according to the principle mentioned above. No, this is not possible.

Back to school!

—SA