I think so.
For this kind of application, you probably want it tight directly to your list of contacts.
Maybe this is the killer application for XMPP based instant messaging ?
OK, I've read Twitter has heart-stopping SMS usage bills (they use 3rd party gateways). XMPP client for OpenSocial/Android/iPhone anyone? We need to break the strangehold of SMS/Phone company gateways.
I would like to write an XMPP client at least for the iPhone, but we are waiting for the native SDK from Apple.
For Android, we are waiting for the first devices.
But sure it will come.