I've used Viorcoin to make a call and I must say I am impressed with the sound quality.
But I think the UI needs to be enhanced and simplified. Probably the dev is already thinking about this.
I think the calling functionality should be front and centre, not the wallet/money functionality. The average user is going to use this to make a phone call, not to stake coins. Put a dialling pad, address book, and video-call screen as the main landing page. Basically make it look more like Tox and less like bitcoin:
Tell us what the calling rates are somewhere in the wallet, priced both in Vior and USD or another currency of our choice.
Give us the steps to make a call right in the program, not just buried in a forum.