I just discovered, for my great surprice, that I can send instant messages using the vanilla Diablo SIP client to other Nokia tablet using SIP. We both have Sipphone (Gizmo) account. I'm wondering if it is "normal" to have instant messaging working through SIP?

Gizmo does have its instant messaging, so it could be that the Sipphone proxy is special case to support this. Maybe someone else with "vanilla SIP proxy" can try this?

(And just a reminder that video calls between two tablets using Sipphone SIP service works fine using the built in SIP client... no need to install Gizmo client.)