Remembering my first days of mobile telephony back in 1995, when my Nokia 2148 (aka E-Plus PT-11) was the only GSM1800 phone to support SMS and when SMS was completley unknown and completely free, I became opposed to SMS very soon, when operators started charging it. Against the background of SMS being an incidently emerged by-product, that is realized through control channles at no extra cost for the operator, I reduced SMS-communication when voice-tariffs came down and I realized calling is mostly cheaper and more effective than exchanging a couple of texts.
IM is a very interesting thing, not only because of the costs, but also because the interoperatbility with computers. But only as long as operators don't block IM-services, like those wankers recently started to do over here. They obviously will do everything to prevent becoming sole so-called "bitpipe-providers", including developing their
own IM-service by a GSMA-initiative in order to replace SMS and to bill us for every bit transmitted. VoIP has been blocked here, too. So as long as VPN is not blocked yet, we need to tunnel our communication to some VPN-gateway and that only few people will be able to do.