I once was a contractor at a nameless mobile provider. I know for a fact that every message sent, while deleted from the main system, was archived to a stack of DVD-Rs. They did this for liability reasons, albeit, unofficially and secretly. Every developer could read messages and see which account each message came from. Very entertaining stuff.

Some of the gems included parents scolding their kids, pimps telling their "girls" that the cops were on their way, SMS Casanovas sending the same text to twenty different women, e-bullies, and even people in jail texting their loved ones. Winning ones were shared over corporate IM, also retained indefinitely.

Be smart and assume that everything you ever do, including the email & text messages you write, is archived indefinitely somewhere. In a digital world, it's simply too easy to do and not enough checks and balances exist to enforce data retention policies. If a big telecom is found to be in violation, it's hardly a slap on the wrist. After all, why would law enforcement slap the hand that feeds them this kind of info?

Do they at least get compressed or are just sitting there as is. So much data would take a lot of space. In the former case, I bet a search query takes a long time. Off course I am sure its all RAIDed as well.