Whatsapp after coming for PC  made its biggest release by adding a Voicecalling button to its app

Whatsapp Voice Calling

According to Redmondpie up till now only iPhone has got that update and according to Mashable
They are voicecalling for android which means it will be soon available for android also.

Whatsapp Voice call on Nexus 5
Testing 
WhatsApp CEO Jan Koum announced the feature was in the works last year during Mobile World Congress, though we’ve heard little about it since.