Siemens Gigaset SX762

Overview
More info and pictures here.

Only firmware version 4.x.x.x.x devices are described here (that is, v2 devices).
 * Per the OpenWrt wiki, v2 devices have part numbers following the S30852-S70x-xxxx pattern

S30852-S706-R321-5 may be a valid Siemens part number for this device.