Voice Over IP Software

So for those of you out there that dont know what VOIP is, you can read about it here.

BUT for those of you that do and that have or are using VOIP in your comms mix, I'd love to know about your experiences with any 'softphones' you have used...the desktop or device software that facilitates VOIP calls.

I personally have trialled 6 or so VOIP clients for Mac OSX and I finally settled on one called X-Lite.

Version 3 of the software (pictured above) was a cute and functional software solution. However, since the update to Mac OSX.6 (Snow Leopard) the V3 softphone stopped working.

X-Lite 4 Beta was released and I updated to that but I find it incredible that the updated software is significantly poorer in terms of User Experience than it predecessor.

Simply moving between missed calls, contacts list, redial, previous calls and simple functions are a pain in the ass, requiring the use of application level menus and nested options.

So, I'm asking everyone who has experience with this type of software to make a comment about what they have observed and experienced.

Why? Well I'd like to design my own VOIP solution - for both desktop and device deployment and I'm taking in experiences, wishlists and suggested features/functions.

Thanking You.