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Some Beeper users say Apple banned their Macs from iMessage
(9to5google.com)
This is a most excellent place for technology news and articles.
WhatsApp was available for Blackberry, Symbian, and Nokia Series 40, and I've seen device support cited as an important part of its early success. It actually looks like Skype, AIM, and ICQ had pretty good support for various devices in the early 2010s too so I'm not sure that claim holds up.