Instagram is trying to become the place you connect with everyone, regardless of the medium you want. You can share images and videos with your followers, post ephemeral stories or keep them in your profile, direct message people for private chats, and go live to share your current activity or whereabouts with friends. But that doesn't seem to be enough as the app might be working on voice and video calls as well.
The news was first spotted by TechCrunch who got tipped about the Instagram APK file containing multiple icons for calls and video calls. I verified it on my end by grabbing the latest Instagram alpha v36 file and digging through it to find many icons for calls in the same vein as Instagram's icon design, plus several layouts that mention calls and video calls. It's not known when this will hit, but if Instagram manages to launch this before Snapchat, it could solidify its lead even further.
I am not sure how I feel about this. Part of me is thinking, "oh well, if people on Instagram want to call each other, then why do they have to switch to a different platform to do so? And it's not like anyone is being forced to use it" and the other is replying, "but we have 200 ways of calling people already, two of which are already owned by Facebook, so why add another?" I do understand that users on Instagram may not want to share their name/phone number to be reachable on other platforms, but if every social app is going to add its own call options, we're in for a heck of a ride.