Paul, we use VIBER instead of skpe on our trips. we find it works better, and is also free.( Providing each person has it on their device)
we have been using it every day for the last month to talk to our daughter who is travelling in Europe at the moment.
we often use it at home for the same purpose. at home we have found that apple face time works even better. ( for poor wifi)
we use VIBER extensively on free wifi. we find that most of the time the free wifi is not good enough to be successful for video but voice and particularly texting works good.
the feature that I like the most is that I can send messages, video/voice etc at any time and they sit there and the person at the other end can see them when they next get wifi. perfect for travelling with time zones etc. also there is no time delay, you wouldn't know the person is on the other side of the world.
we haven't used the viberout feature to call landlines, so can't comment on how much it costs etc.
a tip, give it a try at home with a friend, before you go.
hope this helps.