Track App usage in Mobile

This functionality is already inbuilt into Android.

1. Open your dailer
2. Enter *#*#4636#*#*
3. Select Usage statistics
4. Sort by Launch Count.

As far as I know these statistics get reset every time you reset your phone. Hope it helps.

IMEI Number - How to get?

Every phone or Mobile Broadband device has a unique 15 digit code, called an IMEI number.

•  Enter *#06# 

Will get unique 15 digit code.