On the crowded morning metro in Helsinki, silence prevails. Everyone is hunched over their smartphone screens, reading the news, checking emails or watching videos.

A loud "yeah!" breaks the quiet, along with a delighted squeal from a toddler whose mother has just handed him her smartphone to calm him down with a video.

Finland, once a world leader in mobile telephony with Nokia, is in a class of its own when it comes to internet usage on smartphones and tablets, thanks to cheap subscription plans.