You have to download an application on your oeraonal device. There is no voice chat for italki. A lot of people use Skype and Whatsapp
you should try sharedtalk.com
i found it a few weeks ago. completely free, easy to use and there are hundreds of people online from all over the world. i found a few people who i actually practice chinese with regularly.
love the site :D
Find someone on the website that appears to be the kind of person you would like to practice with.
Click on that person's picture or name. Find the FOLLOW menu and send them a private message,
asking if they will practice with you. If they accept, exhange "contact" information in the form of a Skype ID (and do not publish this in the Italki Forum.
Arrange a meeting time.
I use skype with my students.
I have just sent you a request with a message. I teach at an international college in Oxford. Happy to help.