Linux Soft Phone Roundup
Linphone

Linphone Main Window
Linphone is actually a pretty good soft phone. It supports multiple accounts, has a good codec selection (for both audio and video including H.263), a fairly decent UI and is fairly stable.
I wasn't thrilled with the interface though. Hiding it in the task bar requires you to close the window, and when bringing the window back up, it always defaults to your contact list, not the dialpad. It also requires you to click on the "SIP address" text entry box in order to dial unless you double click from a contact.
It also has the annoying habit of displaying video in a separate dialog style window that you can't close on its own. There are also no global hot key selections to allow you to answer a call without using the mouse.
It does have good NAT support and supports STUN and never failed once to make or receive a call. It is quite stable and I have not had it crash on me yet.
The UI is what really turned me off of Linphone, though. It seems more like "business application" than a soft phone, if that makes any sense. Its functional, and things are logically organized, but it doesn't feel like a phone. The extra mouse clicks to get to the point where you dial are also quite annoying.
Beyond the above, it functions well. I was not able to establish a video call between Linphone and anything other than another Linphone, though.
Linphone Conclusions
While its a solid soft phone, it just doesn't feel right to me. The UI is a bit to big and the use of tabs seems out of place, especially when the default tab is the contact list and not the dialpad. It has no global hotkeys but does still manage to integrate fairly well with the Gnome desktop. It will be worth it for me to revisit Linphone in the future to see how it has progressed.
Finally I also looked at QuteCom.
