What about android clients for this?
In general, the reason for the slow adoption of SIP beyond just pure voice telephony is that the SIP/SIMPLE standard with its companions for buddy lists etc. is really crappy, and as a result so are most clients (or the interoperability between them). It doesn't make it better that the mobile device/equipment vendors forked off their own OMA standards, so the situation is pretty bad in that regards.
I still don't give up all hopes to see a proper Android/IOS SIP client supporting voice, video presence etc. while at the same time adhering to the standards.