While true, prior iMessage it was only green bubbles. However, iMessage was released with iOS5 and iOS5 and every iOS prior apple went flat, used very different green: https://www.zdnet.com/a/img/2014/10/04/9ddbf98c-4b94-11e4-b6...

Now compare it to green bubbles today. Anyways, when I had iPhone, flat green bubbles annoyed me. Not because "hurr-durr I have a iPhone and you don't" but because SMS lacked many features and was hella slow to send. Plus, pretty much anywhere I lived I had horrible cellphone reception which made sending SMS a nightmare.