Hey, Agnes from Truecaller here to clarify.
We are not partnering up with WhatsApp. This is an enhancement of our Caller ID where we'll be able to identify unknown numbers coming in from other messaging apps - like WhatsApp.
That way we'll be able to warn you about a potential scam even if it's coming in from another app. It will work even if the call is coming in from other countries - like Indonesia as we've noticed an increase in scam calls coming from there.
The feature is in beta right now. Let me know if you have any more questions or want me to clarify the weirdness in that you still think we upload contacts even though that would be in direct violation of Google Play and Apple Appstore guidelines and our app would be long gone.