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:
Do you have a Skype trick up your sleeve? Share your Solutions and Tips with us!
Favorite Tip for This Week: Do not accept contact invitations from anyone whom you do not know.