A new firmware update for the Lumia 625, Lumia 925 and Lumia 525 started to roll out just over a week ago for a few users and with it came a small, but useful feature: static IP. The ability to set one's particular internet gateway and IP details is something nuanced, but essential for some users on various networks. Windows Phone's ability to support static IPs is as far as we know dependent upon the phone manufacturer as the OS itself does not have this baked in.
The firmware itself is slight, coming in at just 18 MB. It bumps the revision number from 1425.0002 to 1425.0003 on most devices, bringing the new static IP option, network+ option and some bug fixes, according to reader of the site Vinod K.