Comes down to $$$. Carriers should make things simple and make these services inclusive.
Reading a piece from Open Mobile Alliance there is, in the protocol a way to charge, (of course)...
http://www.openmobilealliance.org/te...20050301-a.pdf
Page 27, section 6.5
6.5. Forwarding of Multimedia Message
The forward transaction consists of the M-Forward.req message sent from the MMS Client to the MMS Proxy-Relay in order
to request an MM to be forwarded that is located at the MMS Proxy-Relay and the corresponding confirmation message (MForward.
conf) sent from the MMS Proxy-Relay to the MMS Client.
The request for Reply-Charging SHALL NOT be forwarded. The MMS Proxy-Relay MAY reject a request to forward a MM
that includes Reply-Charging fields or the MMS Proxy-Relay MAY accept the forward request but it MUST remove the
Reply-Charging fields from the forwarded MM.
The MMS Client MUST include a unique transaction identifier in the M-Forward.req message.