This is my favorite quote about the life: "You'll make enough to get by, but if you should ever meet someone and get married, which frankly is going to be damn near impossible being gone so much, you won't be making enough to fully support a family. Your spouse will be a de facto single parent most of the time, and that will always be a source of friction in your life. So, in addition to accelerated aging due to the inhuman schedule, dying of cancer early due to increased radiation exposure from spending 1000+ hours a year in the upper atmosphere, you can also suffer alone due to lack any lasting human relationships beyond what you can rent in Wan Chai."
1) No, we aren't allowed to use the SATCOM to call anyone but the company or air traffic control due to costs. Yes, it is possible to call anyone on a plane with SATCOM, which most have these days. I don't know what kind of equipment it takes to call the plane, as I'm only ever on the receiving end of the call.
2) It's really not much different at all. There is less stress about delays on freighters. There is slightly more work on a freighter as we are responsible for checking main deck cargo security prior to departure whweras on a pax flight the f/a's would take care of that part of the airplane. On the other hand there are PA's to make and a few other human comfort items to consider on pax flights.
3) As someone who flies mostly freighters but occasionally passengers, I really have no strong preference. Most pilots where I work prefer freight but some prefer pax. The pay is the same either way. I have a slight preference for freight because I enjoy the independence of going to the lav and making my own coffee without being babysat. No, we don't go to the main deck (cargo area) in flight because it is forbidden by policy.