Is there a chance you publicly reveal your other IM contacts? Because as it stands I pretty much never get spam on Instagram, Whatsapp, Line, nor Messenger (FB). I don't even get spam in the "Message Requests" of FB messenger.
I get spam all the time on Instagram. Even the private account of the two that I have constantly winds up in random group spam messages. I'm assuming some spammers use scripts or other code to just comb through tons of high-profile account pages' follower lists and then randomly groups userid's to send mass messages to. It's completely frustrating.
The thing I wonder about iMessages, and Apple, is how I don't get spammed at all with iMessages when I have my ID linked to my normal email addresses, which do get normal email spam. You'd think spammers that do email spam would also be smart enough to try sending to iMessage accounts using those email addresses. But I'm guessing it's a limitation on the sender-side vs. the client side and maybe it's not easy to do due to how iMessages is such a closed-system.
The biggest problems are email and phone, which are the two most open systems. I get a decent amount on the ones you listed, but it's not as bad. A few messages a week on each. Most of those have ads, though, too. Different issue, but same problem... a cheap, unavoidable way to force me to see your message. iMessage is the only inbox I feel like I control. No spam, no ads, just friends.
(Not the point, but I'm looking at my Instapainting as we speak! One of my favorite things I own.)
