1.Download latest version of whatsapp from whatsapp official site.
2.You need latest version of whatsapp.apk for voicecall activation.
Activating Whatsapp Calls.apk
1. Install Terminal and open and type the following code
Type : su after typing you will gaining superuser permissions.
Then type below code:
am start -n com.whatsapp/com.whatsapp.HomeActivity