WSJ writes about mobile Instant Messaging:
Unlike text messaging — known as short message service, or SMS — MIM features “presence” services that tell a user if and when their buddies are on the network. It also allows instant delivery of messages, and MIM users can chat in groups rather than just one to one. In addition, MIM allows users to communicate using aliases, whereas text messaging reveals the sender’s telephone number.
With the technology in place or getting there shortly, what has taken wireless operators so long? No small matter for cellphone companies is deciding how to market and price instant-messaging services in relation to text messaging.
“I believe that the biggest reservation that mobile operators have about IM is the danger that it might cannibalize or otherwise damage SMS revenues,” says John Delaney, a principal analyst at consultancy Ovum Holdings Ltd.