Just for clarification, RFComm is SIP although it is in beta it works well. Because it works so well I never bother with Gizmo.

IMO RFComm also makes Gizmo somewhat redundant because it permits choice of SIP provider.

I can understand the necessity of using Skype to call locked-in-to-Skype contacts but isn't Gizmo simply another SIP provider?

However, if there is a technical benefit to using Gizmo, e.g. call quality, then that would make a difference.

My experience refers to PC and N800 only.