A lot of the people out there using iMessage don't even know it. Because it hooks in so transparently with text messaging, people who used to SMS between iPhones now iMessage between them and many don't even realize that anything has changed.
Among those who do know the difference, my experience is that by far the most common reason to use it is to avoid paying for text messages. (I'm in the US here, so it's common.) A secondary reason, but really secondary compared to that, is the fact that it works on other iDevices, not just iPhones.
Until I read these comments, it didn't even occur to me that security might be an advantage of iMessage. I think the number of people who use iMessage because of that is roughly zero.
Among those who do know the difference, my experience is that by far the most common reason to use it is to avoid paying for text messages. (I'm in the US here, so it's common.) A secondary reason, but really secondary compared to that, is the fact that it works on other iDevices, not just iPhones.
Until I read these comments, it didn't even occur to me that security might be an advantage of iMessage. I think the number of people who use iMessage because of that is roughly zero.