Every now and then I travel the world and stay in places where I'm charged 2.50 Euros a minute for the privilege of making traditional mobile voice calls with my mobile phone to someone back home. Needless to say that long calls for €150 per hour have to be avoided if at all possible. These days, however, Skype or other VoIP clients that run on smartphones come to my rescue in combination with a 15 Euros for 150 MB roaming data package.
So what's the price difference to those 2.50 Euros a minute circuit switched mobile calls? When not using video, Skype uses around 20 kbyte of data per second which is around 72 MB an hour. In other words, that 150 MB data roaming package for 15 Euros buys me around 2h worth of Skype calls, i.e. a Skype call to another Skype user costs me €7.50 when roaming. When used to call a fixed line phone, add a euro or two. In other words, despite using an expensive data roaming package, that Skype call costs 20x less and I'm sure my home network operator still has a good margin on roaming data. Hour long mobile calls 10.000 miles away from home have just become sweet again.
And a nice bonus: When calling other Skype users, voice quality is way beyond what's possible with circuit switched mobile calls between networks and continents. No WB-AMR anywhere… The only downside: Should your connection drop down to 2G during the call that's rather an abrupt end of the conversation. So in mobility scenarios, circuit switched mobile calls still have an advantage, at least until that 98% coverage requirement is reached.