WhatsApp is internally developing group voice calls.
With group calls, you can call multiple people at the same time. The feature is long-awaited as competitive apps like Skype have been supporting group calls for a long time.
WABetaInfo discovered today the first references for group calls in WhatsApp’s source code. Because these are only references and the function is not in test phase yet, it will probably take months before we can use it.
Whether it’s also possible to start group video calls in future is not known yet. This would obviously be a logical follow-up step.