I am sadly, somewhat of an expert in this regard.
I use Talkatone, and have for years, on a myriad of devices. It's now reliable, the audio quality is terrible, and I keep falling back to a real phone. I have a 5S, and a mini, and my mini retina just shipped and will arrive Monday. I am hoping that three things in the updated model will improve the overall experience on the iPad. 1. A much faster CPU (A7). 2. Noise canceling dual microphones. 3. Mimo antennas.
Turning off Wifi and using LTE or even 3G yields the best call quality through Talkatone presently. Counter intuitive? Yes, but this has been my experience, again, over years and a myriad of devices. I have 3 or 4 times tried to live out of Talkatone, or the othe VoIP apps, and it's just not possible. They are all sub-par. Nothing is going to be as good as a real cell phone call, with the possible exception now of FaceTime Audio calls, but then the recipient must have a iDevice running iOS 7.0.4 and have FaceTime correctly activated.
I will report back to this thread in 2 weeks to see if there's any improvement. I doubt there will be, ftr.
And why, why, is this the first place online I have ever found that stops Apple's built-in spell checker from working? And ironically, it's Apple's own site. How, so, VERY typical. *SMDH*