We have an example application in our Symbian Downloads section named "SMS Example Application". This is an example for the 9200 Communicators but you can use the same code, that is used for reading messages, on a Series 60 Platform as well.
See the code in class CGDSMSAppUi::MessageReceivedL(). It shows how to load a message into the MTM and how to read it.
In CGDSMSAppUi::HandleSessionEventL(), there is some pointers on how to read message entries to/from an entry selection object and how to retrieve actual etries with the CMsvSession pointer.
To your comment on my previous reply: the etelgprs.h header (in Series 60 SDK) is not public for 3rd party developers. Unfortunately this breaks the SMS MTM API since the SmsSettings header is using it. We are working to get this situation fixed.