[randomdata]

On iPhones, you don't explicitly use iMessage, it just switches to iMessage automatically when sending an SMS message to a recipient also uses iMessage. That is the primary reason to use it, though it is handy to be able to send messages on the network via other Apple devices as well.

[aerique]

I had to turn iMessage off on my iPhone since it was extremely flaky for me and an acquaintance: messages would not be delivered or much later. WhatsApp is better but SMS has been the most reliable so far.

This is using T-Mobile in the Netherlands.