When it comes to data retention, most of us know by now that there are multitudes of different people who hold on to your “private” data for various reasons. Of course, this is why your “private” data isn’t really “private” at all, when you think about it.

Carriers like AT&T, Verizon and Sprint play a huge role in most people’s daily lives. Just think about how often you text, make a phone call or surf the web from your mobile device. You are constantly using the provider’s service to function in your daily life – it’s unavoidable.

So just how long does a carrier hold on to the data it gathers about you? A leaked memo shows that it really depends on the carrier.

Wired has obtained a one page Department of Justice document called “Retention Periods of Major Cellular Service Providers.” They obtained it from the ACLU, who obtained it via a Freedom of Information Act claim.

The document is dated August 2010 and says “Law Enforcement Use Only.” So this document could possibly have been used by police and investigatory organizations to better understand how to pursue data collection from mobile providers.

After looking over the document, it’s hard to make a determination as to which carrier is the best when it comes to user privacy. Each carrier does something better and each carrier does something less desirable than the next. Here are the highlights –

• Subscriber Information: Verizon, 3-5 years.  AT&T, depends on service length.  T-Mobile, 5 years.  Sprint, forever.
• Call details (who, when you called) – Verizon, 1 year.  AT&T, 5 years for prepaid 7 years for post-paid.  T-Mobile, 2 years prepaid 5 years post-paid.  Sprint, 18-24 months.
• Text Message detail (who, when): Verizon, 1 year.  AT&T, 5-7 years.  T-Mobile, 2-5 years.  Sprint, 18-24 months.
• Text message content: Verizon is the only one who keeps this information, and they do it for 3-5 days.
• IP session information: Verizon, 1 year.  AT&T, only on non-public IPs for 72 hours.  T-Mobile, not retained.  Sprint, 60 days.

The same goes for IP destination information, except Verizon only keeps it for 90 days.

Wired quotes an ACLU lawyer who says, “People who are upset that Facebook is storing all their information should be really concerned that their cell phone is tracking them everywhere they’ve been. The government has this information because it wants to engage in surveillance.”

Facebook came under fire this week for a situation involving tracking cookies that were found to still exist even after users log out.

The fact that carriers know and keep this information shouldn’t shock anyone. But some of the periods of retention in the document are interesting. If there is anything to be gleaned from this, it’s that everything you do sticks around, probably for longer than you think.