What kind of SOAP messages is visible in IDispatchMessageInspector?

Hello

I extended behavior with implementing IDispatchMessageInspector. I am
wondering what kind of SOAP messages can I see here. I know I can
extract calling function and response, faults (what about events,
callback operations?). And I think messages for security, transactions
and reliability are no longer visible at that point. Are they visible
only to chanels (where exactly)?
Is it matter which message encoding (text, binary, MTOM) is used, if I
want to parse message in IDispatchMessageInspector or are all messages
alredy in text there?

I hope you understand my question. Thank you.