And about 100 TB a day as of 2014 - so lets triple that.
And assume 300 TB per day in messaging
And lets divide that in two for between iMessage and sms
But since android tops ios in global qty of devices..
Lets double it. And where in the past the Philippines was known to be the top users of sms, but with ayala scaling up over the last years... lets quadruple that number and so i would estimate 600 TB a day in just iMessage and sms alone.
I love this. Reminded me of one time some 15+ years ago I did some back-of-the-envelope math like yours but on people using colored characters on every message on IRC w/ scripts and how much meaningless data that generated... it's astonishing how quickly you can get to the PB scale
So lets assume that amazons cia/nsa op datacenter is receiving these 1PB a day messages.
Lets assume they use a tool to remove certain very common words and an algorithm whic can replace the hidden words later if they want to restore the messages.
Text compresses really well.
And if you have a replacement dictionary, even better.