This graph shows the number of minutes people use to talk on the phone, from 2005 to 2012. The y axis is in millions. The people make phone calls to other countries, hence the word 'international'.
The graph tells us that over the last few years, the number of minutes used to talk on the phone have increased tremendously. From 2005 to 2007, the increase has been gradual, not too much. In 2008, the numbers took a turn and it increased the most, of 3133 minutes. From then on, it has been increasing ever since.
The cause of this is most probably because over the years, Singapore has expanded its business throughout the world. Singapore may have many business deals with other countries and thus, the number of minutes spent talking to foreigners overseas has increased tremendously.
Another cause of it would be because Singapore brings in foreign talent and at the same time, domestic helpers. They still need to keep in contact with their family members, so they would call them, on average thrice per month, that would mean 36 times a year. About 10% to 20% are foreigners. With the large amount, it would definitely add to the total number of minutes.