The new record was set when Karjalainen flung an old Nokia handset an astounding 101.46 metres.
This was the first-ever throw in the history of the Championships that passed the 100 metre mark, and was 17 metres farther than the throw than brought a gold medal in the javelin event at the London Olympics.
Karjalainen told the Reuters news agency that he had had only a single practice throw before the event, and that he prepared for the Championships by "mainly drinking".
The young Finn triumphed in a field of about 50 competitors, some of whom came from as far away as India.
Second place was taken by Jeremy Gallop of South Africa with a throw of 94.67 metres, which set a national South African record, as well.
The winner in women's category, Jonna Mattero, is also from Finland. Her result was measured at 42.47 metres. The juniors' title was taken by Aleksi Muukkonen's throw of 39.19 metres. The freestyle event was won by Santeri Patrikainen with a cumulative score of 12 points.
The Mobile Phone Throwing World Championships have been held every year since 2000 in Savonlinna in late August and has led to a series of official national championships all over Europe.