Operators can allow to install Windows Phone software updates without data charges. Windows Phone 8.1 GDR1’s latest update may have brought the ability to enable zero-rating download for device updates. This means users will be able to install software update on their Windows Phone device without incurring any data expenses.
It seems that after the update Update 1 Windows Phone 8.1 the operators will be able to let us unload system updates using the mobile network without affecting our data limit . All phones are compatible with this feature, either free or carrier.
The size limit for these updates is 100MB , but the operators can expand if they wish.
What is Zero Rating:
Zero-rating allows users to download data, such as device updates, without being charged for data usage. Mobile Operators (MOs) can enable and test Windows Phone updates to work with zero-rating.
The method used in this topic prevents updates for non-Windows Phone devices connected via Internet Connection Sharing (ICS) from being zero-rated.
According to OEM Documentation
Add the following two URLs to your network as zero-rated sites:
Once those URLs are zero-rated, there are no more actions to take to get zero rating in place. It will be effective for all Windows Phone devices (both operator variant and open market devices). The first eligible update for zero rating is Windows Phone 8.1 GDR1.
To test zero rating activation, you’ll need to trigger an update over cellular which is small enough to stay under the limit defined by your MO.