There are still a few months to go before the standard HTC One gets upgraded to Android 4.4, but in the meantime, Sprint is rolling out a minor OTA to the aluminum-bodied flagship. This update addresses an issue following a previous upgrade where users were presented with a "No SIM Card" message informing them that 4G LTE will not work without the required card. The phone should now also more accurately display how strong a radio signal it is picking up. These fixes are joined by an HD Voice improvement.
The software update is version 3.05.651.3. You can check manually for the software update, or you can simply wait for it to come. There's little that's urgent here for the majority of users, but updates are updates.