My daughter is stationed in Japan and we use Facebook video chat and calling.   As long as she has data it doesn't cost and believe it or not the quality is actually pretty good.    

We also use Facebook messenger to send messages and pictures back and forth.

Hope this helps.

My daughter was just in Greece for 3 weeks and we have Sprint they have an affordable plan for that area. She texted me and her friends constantly and posted pictures on Facebook called me several times never went over limit.

My son has been in the Navy for 7 1/2 years now and he only uses Facebook messenger, or calls me through Facebook or Skype but that's because he is in and out of different countries.

I can understand your son wanting a phone plan when he is there. Like with my daughter we wanted her to have a phone for emergencies and I think he will have to have a phone for his superior to reach him when needed.

Take care, Paula

My son had Verizon and when overseas used Skype in wi-fi areas. Facebook video chat is now available and also used in wi-fi spots.