I bought iPhone 4 and 5 from Saudi Arabia. Currently, I reside in India. My friends told me that, there are FaceTime and non-FaceTime iPhones, and i have bought the latter ones. So, is there any way to make FaceTime available in these phones?

No unfortunately not.

Facetime time is in the software, there are not different model numbers for non-Facetime phones. If your country doesn't support it, there is no way to get Facetime there.

You're wrong - there are different phones that do not have Facetime. They are sold in the Middle East.

http://support.apple.com/kb/HT3939?viewlocale=en_US&locale=en_US

They have same model # with additional letters on the end.

Certain Countries in the Middle East including Saudi Arabia and the UAE prohibit the usage of facetime. As such and to comply with government regulations in those countries, Apple removes Facetime from all devices sold there.

Since Facetime is part of the iOS software there is no external way to install it on those or any phone for that matter.

The only choice is to use a different service such as Skype for video calls. Skype can be downloaded from the App store.

http://support.apple.com/kb/TS3367

If FaceTime is not available in Settings: Note that FaceTime may not be available on devices purchased or used in certain countries, including Saudi Arabia and the United Arab Emirates.

I think we are arguing semantics. Phil is right, it's not a different model numbered phone. The software is removed from the phone and can not be put in the phone.