The use of instant messaging applications in mobile networks has largely increased in recent years, replacing traditional messaging applications (SMS, MMS). WhatsApp is the application of this kind with the greatest market share worldwide, as a consequence, mobile operators are becoming growingly interested in understanding its underlying functioning and growth. In this paper we revise some of the results presented in our previous work on WhatsApp characterization, and extend this analysis to the new WhatsApp calling service. We study how the underlying WhatsApp architecture has changed after its acquisition by Facebook in early 2014, and shed some initial light on the new calling functionality, active since mid 2015. While the main backbone of the WhatsApp service is still hosted by the same cloud provider -- SoftLayer, we uncover the usage of Facebook servers to support and implement the calling service.