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