Telegram is the latest messaging app to get a major new feature, but unlike Facebook Messenger, WhatsApp, Viber, Hike and countless others, it isn’t cribbing from Snapchat. That’s because Telegram is introducing voice calls.

Admittedly the company is a little late to the audio-calling party, but that is likely because of its focus on security, and in particular end-to-end encryption, which Telegram said also extends to cover audio calls.

Telegram was founded by Pavel Durov, a Russian entrepreneur who rose to fame as the founder of VKontakte, Russia’s Facebook. Since being ousted as CEO in 2014, he has lived a nomadic existence and focused his work on developing Telegram, which gained global attention as an alternative to WhatsApp after it was acquired by Facebook in 2014. WhatsApp now has more than one billion users, making it the most popular chat app on the planet — when we last heard from Telegram in February 2016, it had clocked a lower (but nonetheless impressive) 100 million monthly users with 350,000 new users joining per day.

Those users will soon gain access to Telegram Calls, which the company said is rolling out to those in Europe first before coming to the rest of the world soon after.

These days, most messaging apps have audio and video calling, so how is Telegram aiming to stand out?

Call quality is one focus.

The company said it is using artificial intelligence to increase quality on an ongoing basis. Telegram said its AI uses various call information, such as network speed, ping times and packet loss percentage to optimize each call and learn for next time. That, it said, can improve the quality of calls as more time is spent talking via the feature.

Elsewhere, there are some useful granular control options that allow users to choose a “low data” call — saving on a data plan at the expense of poorer call quality — while the app lets users limit things so that only people in their contacts can call them.

Then there’s the encryption. Telegram said the framework for its “Secret Chat” feature has been adapted for this new introduction.

“Telegram Calls are built upon the time-tested end-to-end encryption of Telegram’s Secret Chats. The key verification UI we came up with in 2013 to protect against man-in-the-middle attacks served well for Telegram (and for other apps that adopted it), but for Calls we needed something easier. That‘s why we’ve improved the key exchange mechanism,” it said in a blog post.

In practical terms, that means that two people making a call over Telegram will be able to compare four emojis as a key exchange to ensure that their call is encrypted. That’s a more fun take on random pairing words or long passcodes on other secure services such as Signal.

Telegram posted more details on the security behind the feature in a Q&A here. That’ll doubtless be of interest to many in the security community who have been vocal with their criticism of Telegram’s cryptography.

In 2015, mobile security firm Zimperium concluded that Telegram’s system “will not stop sophisticated hackers from reading your messages.”

“Telegram is error prone, has wonky homebrew encryption, leaks voluminous metadata, steals the address book, and is now known as a terrorist hangout. I couldn’t possibly think of a worse combination for a safe messenger,” security researcher The Grugq wrote in a blog post later that year.

Those opinions are particularly of interest since Telegram has become a popular app among ISIS, according to media reports. Telegram itself has booted ISIS-related content from its service; it did so after the Paris attacks in 2015 when it learned that its public broadcast feature had been used to spread propaganda. It also made it easier for users to report inappropriate material, but it, and other apps, continue to come under pressure from politicians who perceive that their encryption is aiding enemies.

Just this week, U.K. Home Secretary Amber Rudd singled out WhatsApp, which introduced end-to-end encryption as default for its conversations last year.

“We need to make sure that organizations like WhatsApp, and there are plenty of others like that, don’t provide a secret place for terrorists to communicate with each other,” she told BBC journalist Andrew Marr in an interview.

“It used to be that people would steam open envelopes or just listen in on phones when they wanted to find out what people were doing, legally, through warranty. But on this situation we need to make sure that our intelligence services have the ability to get into situations like encrypted WhatsApp,” Rudd added.