Skype for iPhone: voice quality great
Voice calls made over Wi-Fi sound very good, though. Skype-to-Skype calls are loud and clear, with quality that is better than your average mobile phone call. SkypeOut calls made to both landlines and mobile phones aren't quite as sharp, but the overall quality is very good, comparable to a very good cellular call.
On one Skype for iPhone call we heard a noticeable and distracting echo, but it lasted less than a minute. The existing SkypeOut rates stay the same on the iPhone.
In all, calls made using Skype for iPhone are of significantly better voice quality than any of the mobile VoIP services we've tested recently. That includes Skype for Windows Mobile and Truphone, a Skype-like service for the iPhone. Skype for the iPhone blows them both out of the water in terms of voice quality.
Skype for iPhone: a few glitches
Skype for iPhone is not without flaws, though. It showed one of our contacts as offline, even though he was connected. (It wasn't until he called that his status changed to show him online.) And the app was occasionally slow to respond to taps on the touchscreen; we sometimes experienced a noticeable delay when trying to initiate or end a call, for example.
You won't find a whole lot in the way of iPhone-only features in this version of Skype. You can use your iPhone camera to take a picture to use as your profile photo, or you can upload a picture from your existing photo roll. But that's about it.
If you're looking for a solid mobile VoIP service for your iPhone, we can easily recommend Skype. Sure, rival services such as Truphone have some features that Skype for iPhone lacks - such as the ability to chat via third-party IM services such as AIM and Yahoo Messenger. But, to us, call quality is what matters. And Skype wins that battle easily.