The Samsung Galaxy Note 3 on Sprint is now receiving a software update. According to Sprint's website, the update is meant to bring software version MJ3. The update however appears to bring the MJ4 software version, though they don't seem to be different. This update has a very small changelist consisting of two items. It will fix a problem with the audio on calls and adds the Samsung Keyboard Handwriting Mode to the phone.Certain Galaxy Note 3 owners have been complaining about hissing, popping and garbled speech during phone calls. This update should put an end to these issues. Keep in mind that while the update is being pushed OTA (over-the-air) it may take several days to reach all the devices in the market. If you haven't yet received the notification that it has arrived on your Galaxy Note 3, you can try to coax it out by going to Settings > General > System update > Update.
source - Sprint | Android Central