Are there any reviews out yet on the echo cancellation? The Nexus 4 suffers from a bug that makes most VOIP apps useless. [1] Even though this should have been fixed by now, I would upgrade to the Nexus 5 if it only fixes this.
The underlying problem of that bug (missing audiofx support) was fixed with the Android 4.3 update. It's up to app developers to make use of the APIs now. See comment #20 on the page you linked in your post, where I describe the issue in more detail.
Thank you, I didn't know it was fixed. I did see your comment before and thought that those APIs still were not accessible. But I've seen good reviews of CSipSimple on Nexus 4 recently, suggesting that the problem may have been fixed.