Here is a summary of my experience with selected softphones:

• Ekiga (Linux, Windows) – Has replaced the gnome-meeting project. Works fine, but allows only one global STUN proxy server. That’s a problem if you want to register to different SIP providers from behind a firewall. The feature has been promised in the next major release, which might take some more time.
• Gizmoproject (Linux, Mac, Windows) – This is lame. Needs lot of memory and wastes CPU cycles. Really slow startup. Does not allow to register to other SIP providers.
• Twinkle (Linux only) – Works fine. Has all features I could think of using. The interface is very basic and could be somewhat ‘cooler’
• FireFly (Windows only) – Didn’t get it to work with other SIP service providers. Freshtel might have stripped this feature in later versions (which I have tried). I wouldn’t recommend it.
• X-Lite 3.0 FREE Softphone (Linux only 2.0, Mac, Windows) – Without firewall it works like a charm but I didn’t get it to work from behind the firewall. It does not support multiple registrations in the free version.
• OpenWengo (Linux, Mac, Windows) – WengoPhone includes some IM functionality (ICQ, AIM, Jabber, Google Talk and MSN).
  Updated: As for OpenWengo 2.0 (can be installed using apt-get): You need to create a Wengo account first as without one they won’t let you configure the whole thing. Although the homepage states that multiple registrations with other SIP providers are supported I did not manage it.
  As for OpenWengo 2.1.1: It works fine with Sipgate accounts (have tried those), but you cannot register at multiple SIP providers.

My recommendation is: Use Skype as long as you can and then switch to Twinkle. Both ‘work’ but Skype has a better interface and does not need any (major) configuration. However Twinkle is kind of ‘swiss army knife’ SIP client. Eventually Ekiga will bring support for giving a proxy for each SIP provider. Then I might switch to Ekiga.

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