Serious but naive question. If you are a VF, do you get to pick and choose the calls you go on?
Usually, yes. Each firefighter is issued a pager (such as a "
minitor"), and, when that FF's company is "toned out", the tones set off a beeping - so that is what you hear. I think youtube has some simple videos of minitors going off. Well, when it sounds, there will be a verbal description of what is the event (EMS, MVC, fire, haz-mat, water rescue, whatever), and the address. FFs will respond to their station. When any apparatus starts responding (chief units will usually have their own vehicle, either truly their own, or provided by the department, so they go right to the scene), the dispatcher will give more information. It can be such as my old department - "Hamburg Control to Big Tree firefighters - simplex alarm of fire at Bethel Estates" - that one has all you need in the original call. Another would be "Hamburg Control to Big Tree firefighters - EMS. 3973 Roundtree. 57 y/o male, chest pain." Then, on responding, more detail, such as "chest pain, difficulty breathing, passed out twice." Or, another is "cardiac arrest. Instructions being given." Or, the "cardiac arrest. Prearrival instructions not being given." (<-- that one is usually b/c the caller is the tiny wife of the old man in arrest, or the victim is cold and stiff).
Now, someone will pipe in and give some idiosyncratic difference that their company does. One thing into the 21st century is that some dispatch agencies have the option to send the call out as a text, so people with smart phones get all the information.
Some agencies with either a tradition, or with difficulty staffing regularly, will have the volunteers in the station, much like professional FFs - except they aren't getting paid. In that case, they'll respond to all calls, immediately. Another is having scheduled people for certain nights, so that those people will take all the EMS calls, and others can safely ignore them, with the others being "on call" for the other nights. There are many ways to do it.
But, to answer your question, the essence of the volunteer is to respond to the calls that you can. Departments that have a "service awards" program (a retirement plan) dictate a percentage of calls that one must make to get credit for a service year. That is a motivation. Also, you'll find that many volunteer departments have young 20 somethings hanging around the hall during the day, because they are under- or unemployed, and just waiting for things to do, so they'll Xbox/PS it until the tones go off. If someone is EMT or paramedic certified, or, during the day, can drive the trucks and run the pump or ladder, then there might be a little more pressure to respond (or individual sense of duty).