In a blog post Nokia Developer offers a few extra details on a new Nokia-specific firmware (1307/1308) for Lumia devices running Windows Phone 8, which is now shipping on new devices and is expected to be made available to existing devices shortly.

For the Lumia 820 and 920 the new firmware (1232.5957.1308.00xx) includes performance and stability improvements (bug fixes), enhancements to display stability during a call (optimisation of proximity sensor), and improved automatic display adjustment (optimisation of ambient light sensor).

For the Lumia 620 the new firmware (1030.6407.1308.00xx) includes improved touch behaviour, stability improvements and improved camera picture quality (e.g.  corrected camera exposure when the flash is used in bright light conditions).

From the blog post:

As part of Nokia’s continuous development practice, we will be introducing new software updates for Nokia Lumia 920 and Nokia Lumia 820. This software, version 1232.5957.1308.00xx, includes further performance and stability improvements, enhancements to display stability during a call, and improved automatic display brightness adjustment.

In addition, Nokia Lumia 620 has some new software in the pipeline. This software, version 1030.6407.1308.00xx, will include improved touch behavior and enhancements to system stability and camera picture quality, such as corrected camera exposure when the flash is used in bright light conditions.

We are starting to deliver the latest software on new Lumia 920, Lumia 820 and Lumia 620 smartphones now. Current users of these smartphones will be receiving the updates to their phones later. 

In addition the new firmware enables a number of features necessary for other, optional, app-based software updates. The most noteworthy of these is the addition of a "storage check" module in the Settings app, which we wrote about earlier this week:

Storage check, which is specific to Nokia Lumia devices, provides a more detailed breakdown of a phone's internal memory than the existing standard phone storage module. It also allow for users to manually delete temporary files, which should help alleviate the "other" storage issue that sees the the amount of space occupied by "other" files, as shown in the phone storage module, grow over time.

Availability

The 1308 firmware is now shipping on new Lumia 920, 820 and 620 devices. It will be made available to existing devices shortly. The firmware is a Nokia specific update and is not tied to a Microsoft platform update. That means the OS version, 10211 (Windows Phone 8 GDR 1) will remain the same.

Once the software update becomes available your device will let you know about any update automatically, but you can also check manually using the phone update module of the Settings app. We'll also post a story once the software update starts to roll out.