Some LG Optimus G users on Sprint are reportedly getting surprise updates to Android 4.1.2 Jelly Bean, the long-awaited system upgrade.

When LG shipped its Optimus G smartphone with Android 4.0 Ice Cream Sandwich (ICS) it left many wondering why it didn't pack the latest Android version. Not that ICS is worthless, but a flagship device usually comes with all the bells and whistles possible.

The official Android 4.1.2 rollout date remains a mystery, but apparently several Sprint Optimus G owners just got lucky. While several users boasted getting the upgrade, the fact that no update was officially announced raises a few questions.

It remains unclear at this point whether this is the beginning of a full-on rollout, or just some sort of testing phase. Until Sprint or LG say something official, however, the second theory seems more plausible. Some speculation hints that LG itself rolled out the 474MB update early, but without an official announcement, it's tough to say.

Nonetheless, the LS970ZVB firmware is out and ready, which means that LG Optimus G users who got tired of waiting for an upgrade can have a taste of Jelly Bean right now. On the other hand, it's worth noting that the handset must be on stock ROM and locked to successfully make the upgrade. Those with unlocked systems can go about several ways to re-lock, most of which are available online. A XDA thread can offer more details.

Other than that, the update should install like any other Over the Air (OTA) upgrade. Note, however, that without OTA Root Keeper's magic users will lose root access when installing the update.

The 474MB update is reportedly legit, and is available on the XDA Developers Forum. The same thread mentioned above also has some good advice for potential issues, which should make things easier.

Meanwhile, Sprint LG Optimus Pro users who don't want to update their device until something official comes up can wait for Sprint to announce the big rollout. Come to think of it, Sprint is a bit overdue on the update, so it may not take long until it officially brings the goodies.