I posted some brief thoughts on SMS and instant messaging a few weeks back which triggered a bit of discussion... and prompted Jag to email me this document - a white paper he's co-authored looking at IP messaging from an operator perspective, and making some suggestions for approaches.

When I last saw Jag he mentioned a Spanish operator who had an interesting pricing model for IM: users are billed one-off at the start of a conversation, but get X minutes of messaging thereafter included into the price. So your typical use cases (short conversations) are still priced at a flat-fee, whilst longer conversations generate more revenue. Good to see there's still room for experimentation here - and that some operators are giving new stuff a go...