Talkonaut is described as 'free Jabber (XMPP) client for your iPhone or iPod with free peer-to-peer voice calling over Jingle Audio extension compatible with GoogleTalk™. Talkonaut can be used with any standard Jabber account like Gmail, Gizmo5™, Jabber' and is an app in the Social & Communications category. There are more than 50 alternatives to Talkonaut for a variety of platforms, including Android, iPhone, Windows, iPad and Mac. The best alternative is Element. It's not free, so if you're looking for a free alternative, you could try Jitsi or Tox. Other great apps like Talkonaut are Wire (Free Personal, Open Source), WhatsApp (Free), Hangouts (Free) and Zulip (Free Personal, Open Source).
Element is a secure collaboration and messaging app based on the Matrix protocol. It’s decentralised to deliver digital sovereignty, and based on an open standard for easy connections and interoperability. It is end-to-end encrypted by default.
Jitsi (previously SIP Communicator) is an audio/video and chat communicator with full encryption that supports protocols such as SIP, XMPP/Jabber, ICQ/AIM, Windows Live, Yahoo!, GTalk/Hangouts extensions, as well as OTR, ZRTP, etc.
Wire is the most secure collaboration platform featuring messenger, voice, video, conference calls, file-sharing, and external collaboration –all protected by the most secure end-to-end-encryption. Why Wire?
WhatsApp is an iPhone and Android messaging app which allows you to exchange messages without having to pay for SMS. In addition to basic messaging WhatsApp users can create groups, send each other unlimited images, video and audio media messages.
With Viber, everyone in the world can connect. Freely. More than 460 million Viber users text, make HD-quality phone and video calls, and send photo and video messages worldwide over WiFi or 3G - for free.
ChatSecure is a free and open source messaging app that features OTR encryption over XMPP. You can connect to your existing accounts on Facebook or Google, create new accounts on public XMPP servers(including via Tor), or even connect to your own server for extra security.