You don't say if you're using an OS or just the base QF which will make a difference in how things are done.
I've done some serial and 802.15.4 networking using the base QF for my sensor-boards.sourceforge.net project. Incoming data is pretty straightforward. I've defined a generic MsgEvt which includes a data buffer. The device drivers fill up the buffer and publish it to the system. Outgoing data is more complicated since the application needs to make sure the driver isn't busy before sending its data (since an active object shouldn't block). Right now the schemes I have for sending are either "best effort" or polling the device at a high rate -- both of which have their limitations.