See also A Brief Introduction to SIP.
See also Gizmo Project Wish List.
Dan just pointed me to the Gizmo Project, yet another player in the SIP field of Voice Communications over the open SIP protocol I keep raving-on about.
Other major players have also been:
Pulver.com Free World Dial-Up: a long-time pioneer in the field.
SIPphone.com: actually powers the Gizmo Project, has been around for a while too.
EarthLink Free Online Calling (which i use): launched in late 2004, opened for free to everybody 2 months ago.
The Gizmo Project appears to be a re-branding of SIPphone.com's original offering, with possibly the most polished SIP Software for Mac OS X around.
While the Gizmo project ostensibly advertises that Gizmo users can chat for free with other Gizmo users to encourage people to sign-up for their service, since it's built on the SIP protocol, the first thing I did was to plug my EarthLink SIP address into the input field: sip:email@example.com. It worked! The key here is that with true SIP providers, any SIP user can talk to any other SIP user by simply using the person's full SIP address:
After some digging around, I found out that any SIP user can call a Gizmo Project user as such:
sip:firstname.lastname@example.org (in my case, sip:email@example.com)
sip:firstname.lastname@example.org (in my case, sip:email@example.com)
Conversely, any SIP user can all any EarthLink Free Online Calling user as such:
sip:firstname.lastname@example.org (in my case, sip:email@example.com)
sip:firstname.lastname@example.org (in my case, sip:email@example.com)
It's kinda wild: I've got SJPhone, a plain SIP software configured for EarthLink SIP and the Gizmo Project SIP software, running at the same time on Mac OS X. Both of them are configured to use my Motorola HS810 headset for sound input/output. And I'm able to ... call ... myself ... hah hah.
Aren't interoperability and open standards loads of fun? I'm having fun! Are YOU having fun?