I can’t remember off hand what happens to the res pilot when flying is appropriated (never happened to me on reserve) but it helps to think in terms that you are not required to carry a cell phone at any time for this job. If you didn’t have a cell phone, you wouldn’t know that your flight was appropriated until you showed up for the flight... unless you voluntarily called them or voluntarily answered a phone when they called you. Whatever they can do to you as a res pilot in this situation (read the LOA), keep that in mind before you answer/return call.