I have skyped my friends via iPhone. If you are on wifi it works well, but that really depends on your connection. Sometimes it is slow and there are a few bugs that need to be fixed. To answer your question the quality is good enough.
I haven't used it on a phone, but I have tried Skype on my tablet. It ran terribly, then crashed. However, Googletalk runs amazingly well on Android, provided both of you have it- available through Gmail.