Telegram for Android OS has a video call function, according to the messenger's blog.
For iOS users, calls will be available after the app update is reviewed by App Store moderators.
To start a video call, you need to click the button with the camera icon in the user profile.
“You can switch between a voice call and a video call right during a call, as well as chat in chats without ending the call: it can be minimized to a small window in the corner of the screen,” the blog says.
Telegram has promised to launch group video calls “in the coming months.”