Hi, Ershadismail, and welcome to the Community,
Skype has not made any announcements about plans to release versions of the Skype app for older BlackBerry OS devices (OS 7 or 6). Skype is now available on the BlackBerry Z10 and Q10 devices running the 10.1 OS update.
For more information, please see these FAQ's:
Online Safety Tip: Change your passwords often!