I tested Gizmo yesterday and this morning:
+ I could play music with XMMS and hear ring tones from Gizmo.
+ I added a contact from Ekiga-net. No problem
- Gizmo didn't have any file transfer.

I guess Gizmo will add file transfer feature in near future. If they do, I'll definitely say goodbye to Skype. Why should I use an old fashioned application using a locked protocol, when I can use SIP? Can't find any reasons. Skype will be dead within 5 years, that is my prediction.

After 5 years:
Skype for windows (new ultra shiny): 10.0
Skype for mac (new! 100000 people conferencing for Intels): 5.0
Skype for linux (fixed packaging issues! download and... a... hm.... promote it to windows users!): 1.2.0.99

After 5 years:

Windows: What's that? That's something you put in houses...
Mac: the new Windows...
Linux: for the oldies to run their windows programs on... (wine etc)