Source is a few years old, but I suppose we can make another FOIA request to find out how long carriers store text messages these days - it was basically 0-5 days a decade ago:
Idk... back in the mid 2000s my parents managed to get a transcript of all of my (minor) sister's SMS messages for a few months back (as part of a billing dispute).
You’ll be lucky if it’s any longer than 24-hours now. There’s no business use case for building and maintaining the technological infrastructure to manage it for years. It’s private info and they can’t sell it to anyone without legal liability. If LE gave them the funds to build this infrastructure and use it for retention then the service provider is essentially an agent of the state at that point.
I can only imagine that the scale of all US SMS messages is absolutely staggering. It probably eclipses all other text formats combined in terms of daily production. Here's a blog post from a few years ago estimating it at 26 billion text messages per day and rising: https://www.textrequest.com/blog/how-many-texts-people-send-...
Not counting media and assuming they are all 160 byte messages, that's 4 terabytes per day, or about 200 wikipedia's per day. I guess that's not too bad in terms of storage requirements, certainly a management amount of data for a telecom to store. But assuming that you want those indexed and easily retrievable somehow, it could get very burdensome to manage and interact with, and that tends to balloon the size at least a little bit as well.
The liability and legal issues around it (both externally and internally - don't want employees spying on their exes, leaking data from celebs, in addition to the policing issues, etc) makes it pretty undesirable to store though.
https://www.nbcnews.com/technolog/how-long-do-wireless-carri...