imo is a free video calling and chatting app that is 95% accessible with VO. It reads hints that VoiceOver will say aloud. For example, if VoiceOver says profile, after 3 sec, it will say views user's profile.
Are all the buttons clearly labeled? Not quite, but don't get fooled. A lot of the buttons are clearly labeled, it's just one of those apps that have some buttons that are weirdly labeled. Again, don't let that fool you, the buttons that are labeled weirdly can still be recognized.
If you want to download imo, I have put the link above. Try it out.
Oh, and if you don't know how to use it, I've got a recording I'll be doing and I will post the link on this forum when done.
Meanwhile, here are some more features:
Video and audio calls to other imo users
Text other imo users
Invite your friends
Audio quality is good, depending on your device