This is exactly it - as a teen I am excluded from class group chats regularly as I don't have iMessage. For group chats, it really does annoy everyone because it's hard to get everyone to switch. I've relied on the fact that I help others with work to get people to switch, and I've only been able to do that for my grade's IB class (15 people) onto Instagram and WhatsApp. It sort of helps that the school is not a rich school, that way there's still others with Androids and I'm not the only one.