Does a channel carry or transports the message?

E-mail

Perhaps a e-mail or a text. Possibly even a little birdy (Birdie). =-)

Hormones act on cells that have specific receptors within the cells that respond to them. So in this case the medium is the message.

The mRNA carries the message from the nucleus to be translated at the ribosome.

they can carry a lot of different things, but the most common is waste materials i think.