VoIP technology is actually now more than 20 years old and the initial boom in consumer wireline VoIP came more than 10 years ago. Wireless mobile VoIP has also been around for quite a number of years. The first consumer application was introduced in 2006. A long time ago in telecoms!
Most people never go anywhere without their mobile these days and there even exists a name for those who experience anxiety when they are without their phone: nomophobia. What's more, O2 claim mobile usage abroad is growing by 100% each year.