As some of my longtime friends inside AT&T will attest to I've been a long time proponent of SoftPhones for VoIP and hammered hard on them to add a soft client to CallVantage from day one. Over time I've played with the CounterPath Eyebeam product and while it was the best of the lot and remains as such, what I'm finding is the customized offerings from GizmoProject and Yahoo Messenger with Voice are surpassing it and because they are tied to IM clients (Yahoo will have a late stage beta for the Mac this month Yippee!!!) with already existing buddy lists and other features (music that stops playing when the call starts) so the concept of convergence starts to take shape.
By convergence, I should really say next wave of collaboration and communications is coming into play. Later this month (I hear May 15-18 range) AOL will have AIM PhoneLine working with their Messenger client, and they are giving away free inbound DIDs, one upping Yahoo and Skype in the process and lowering the barrier to entry to start off with. My guess is AOL will be adding a lot more features as time goes on, just as I expect Yahoo and Gizmo to do the same as they also add more "applications" which to the public will be features, once the get really into the promise of VoIP 2.0 which Brad Garlinghouse and Jeff Bonforte both know is the world they have play in, despite all the internal Yahoo hurdles (corporate politics, technology that is platform wide, etc.) So as far as I'm concerned apps which are features are at the crux of making convergence easier for the end user to buy off on. Once that happens, the new apps become the lightning rod that hyper accelerates VoIP and really takes users away from PSTN or Voice 1.0.
As I have said for more than two years applications are what it's all about for VoIP to be Different. Client David Beckemyer already figured that out with PhoneGnome three years or more when he started to build the easiest to use in the world VoIP and PSTN application platform, which is one reason why iotum is up and running on the PhoneGnome platform today. Others will do the same when it comes to integrating apps like iotum that speed up collaboration and make communications easier, and more efficient, both in cost and time.
As we see fixed mobile convergence rise too, the need for a soft phone will also ascend, and those softphones, especially if they tied to Instant Messaging as that is the easy way into greater adoption!