Not long ago, although it was last year, I discussed the dominant position Skype has in the Voip world. In my personal as well as my professional opinion, Skype will not continue to be the dominant player if they continue their strategy as planned. Another interesting player in this market is The Gizmo Project. Using the open SIP protocol as opposed to Skype's own closed Voip protocol, they now have a bigger perspective as more and more hadrware based Voip equipment has become available for office as well as home use. Another big development for the gizmo Project is the support of the biggest seller of mobile phones Nokia.

Nokia today announced that users of the Nokia N80 Internet Edition will have easy access to low-cost calls over the Internet with SIPphone's Gizmo Voice over IP (VoIP) services.
(Nokia)

This will certainly boost Voip in general, but I believe SIP providers will win the race, certainly if Voip continues to go mobile.....