If I buy an Iphone in Dubai, will I be able to install and use Skype/Whatsapp in other country?
In general, no. Apple performs geographic restrictions (and allots warranty service contact) via the country in which the device is sold and not based on where you take it or reside. In most cases, you don’t have warranty issues, but check the iOS page when you are shopping for iPhone online if you care about getting all the possible encryption, freedom to use any apps:


https://www.apple.com/iphone-7/ios/


At the bottom is usually something like:


  Some features, applications, and services are not available in all areas. Click here to see complete list.


Also, you’ll want to watch where Apple doesn’t even support the device and instead the carrier is used to implement whatever restrictions the government requires:


https://support.apple.com/en-us/HT204042


The note about FaceTime being permanently blocked in addition to encrypted FaceTime and such could easily apply to more services either now or going forward.