WhatsApp is primarily a communication app which lets users send messages back and forth to each other regardless of whether or not they have texting added to their plan, quite simply because it's a chat app which works off of data and not SMS. It's also capable of allowing users to make and receive voice calls, making it possible for consumers to rely more on data than an actual wireless plan. Over the years, WhatsApp has been adding more features to the service to make it much more than just a communication tool, with the most recent being end-to-end encryption for all users.
WhatsApp also added the ability to send documents to users in the beginning of last month, and now it seems that they company will be expanding on that feature a little bit by introducing the capability for users to send ZIP files back and forth. ZIP files are compressed folders which contain a number of files that are usually weigh in at a much higher file size, so adding this capability to WhatsApp would allow its users to send large amounts of files over the network without actually eating up large amounts of data. Instead of sending 300MB of documents, users would be able to compress those documents into a ZIP which has a much smaller footprint and send that instead, using not only less data but also less time.
The ability to send ZIP files in messages is not the only new thing reported as coming to the chat service. WhatsApp is also said to be adding in the ability for users to call back friends or family that they may have missed a WhatsApp call from. This would be possible with the addition of a new dedicated ccallbackbutton that appears next to a missed call making the act of returning that voice call faster and more efficient while also being simpler. Lastly, it's also said that WhatsApp is likely to be getting a set of voicemail options, allowing users to record a voicemail and send a voicemail to other users, although it was reported to be coming to iOS only for the moment, which means Android users may not see this new feature immediately upon launch.