Mobile messaging app WhatsApp has introduced its latest feature that enables its users to make phone calls that are free of charge. Previously, the app only allowed users to exchange free messages with their contacts.

Named as WhatsApp Calling, the invite-only feature is only available in beta version; Whatsapp has opened and closed the invite window for free call beta testers since February 20.

Based on a recent update by Android Police, WhatsApp has closed the invite window last Saturday which may suggest that WhatsApp developers have limited the number of users who can test the free calling feature.

Following the closing of the invite window, there are only two possibilities left- either the invite windiw is set to be opened again or the app will officially release its free calling feature to its users.

For those who are highly anticipating the official release of this new feature or are merely looking for invites, sideloading the free calling feature to their devices can be made possible. Meanwhile, smartphones that run on iOS will only have free WhatsApp calls when the company officially rolls out the feature.

For Android users, they can have the WhatsApp Calling feature by downloading the most recent WhatsApp version available from the official website. After accessing the WhatsApp download page, users should look for the version 2.11.552 of the WhatsApp APK. It is important that installation of apps from unknown sources is enabled in the Settings of their Android devices.

Then again, users can also directly head over to http://www.whatsapp.com/android/current/WhatsApp.apk using their smartphones and download the APK, which can be saved to their downloads folder.

After saving the WhatsApp Calling feature, it should be activated to finally make free phone calls through the app. This can come as a challenge as a user should find another user who has already activated the calling feature on his/her Whatsapp in order to call them. It also remains important to wait for WhatsApp and its activation of invites from its servers.

After making the call, users should restart the app and wait for three new tabs to come into view. These include the new Calls tab as well as the traditional Chats and Contacts tab. Using the Calls tab, these Android device owners can now call anyone on WhatsApp and help their contacts in activating their WhatsApp Calling feature as well.

Despite one’s excitement in finally using WhatsApp for free calls, it remains highly important to be cautious when asking for invites online and avoid fraudsters who set up scams and invite people to unintentionally spread malware.

"WhatsApp will never send you an invite in this fashion. WhatsApp will never want you to complete a survey and download third-party apps in order to give out an invite," The Market Business explained. "Hoax messages are seen going viral, which is sent by the scamster to the ignorant user."