It grew from 2.2 billion messages in 2009 to 4.5 billion messages in 2011. What the future may hold:
[P]erhaps mobile spam will be held down to the level of a minor annoyance for most. But there’s also a possibility the problem will get much worse before it gets better. For a grim picture of the future, one has only to look to China, where unlimited text plans have been widely available much longer. By some estimates, a third of all text messages in China today are spam.