The recent Beeper controversy briefly brought the “blue bubbles vs. green bubbles” topic back into the mainstream. Here’s a brief review for those of you who are (blessedly) unaware of this issue. Messages sent using the iMessage service appear in blue text bubbles within the Messages app. Messages sent using something other than the iMessage service (e.g., SMS, or (soon) RCS) appear in green text bubbles.
The iMessage service and the Messages app are only available on Apple devices. This is usually presented as a competitive advantage for the iPhone. If you want to use the iMessage service, the only (legitimate) way to do so is to buy an Apple device. If Apple were to make iMessage available on non-Apple platforms, that would remove one reason to buy an iPhone—or so the argument goes.
I think this popular conception of the issue is slightly wrong—or right for a different reason, at least. The iMessage service is not so good that it makes the iPhone more attractive to customers. It’s the iPhone that makes iMessage attractive. The iPhone gives iMessage its cachet, not the other way around.