Last week, Apple agreed to encourage VoIP client for Wi-Fi sides of iPhone and the iPod Touch. In fact, I've been promoting that to the FMC companies for several months now.
Well the big news is that several VoIP vendors are working on a client. Truphone, SightSpeed (although the video camera's in the wrong place) are reportedly close to a product. The challenge here is to make it the same quality and UI as the iPhone dialer. In my time at FirstHand Technologies (now CounterTouch) in 2005/6 we tried this with the Microsoft dual mode phones available at that time. Simply, the act of replacing the dialer that came with the phone (which looked bad and worked worse) with a more elegant capability integrated with IM and directory services were much more difficult than it might otherwise seem. It was buggy at best in 2006, but 2 years later, may in fact be farther along.
Surely the iPhone developers have to face exactly these challenges of user experience. Users don't want an excellent dialer in the cellular package and a lousy one on the Wi-Fi side. They want one dialer, with an intuitive UI and highly integrated functionality. This is far harder (from my recollections from 2005/6) than it seems. The OS of these little devices are complex and therefore easy to break. It may not be such a big deal for the iPod Touch which doesn't have a dialer natively (it's not a phone, remember?), but it's probably a huge deal for the iPhone.
