OpenZoep is based on open protocols and thus it is interoperable with other VoIP SW which respect public standards. Here some info about current status:

Gizmoproject

• presence exchange - OK
• chat - OK screenshot
• call Zoep->Gizmo - OK
• call Gizmo->Zoep - NOK, but will be available after we finish SIP in support

GTalk

• presence exchange - OK
• chat - OK screenshot
  
• calls - NOK, as OpenZoep supports SIP while GTalk Jingle. Voice possible after GTalk will offer SIP gateway (if they are going to offer PSTN IN, they will have to...)

OpenWengo

• presence exchange - NOK
  
• chat - NOK
• call Zoep->OpenWengo - NOK, because our current system enables calls only to SIP usernames that are numeric. We will change that, then calls should be possible
  
• call OpenWengo->Zoep - NOK, but will be available after we finish SIP in support

Comparison of two public IM protocols XMPP vs SIMPLE
(SIMPLE is something pushed by Yahoo and Microsoft)

Nokia is active in SIP area...
They offer a free SIP stack and www.forum.nokia.com has a section (Resources>Technologies>SIP) dedicated to SIP and Nokia tools.

First entries appeared in OpenZoep forum today... :)

Stay tuned!