Fon Wireless FON2501A

Overview
This device seems to be BCM5358UB0 + BCM43236B.
 * CPU: Broadcom BCM5358UB0KFBG (SoC, 2T2R 2.4GHz)
 * WLAN: Broadcom BCM43236BKMLG (USB, 2T2R 5GHz)
 * Antenna: 2x external 2.14dBi antennas
 * Port: 1x WAN, 2x LAN, FE 10/100Mbps
 * USB: 1x USB 2.0 Host
 * Buttons: 1x Reset, 1x WPS button

Links of Interest

 * On OpenWrt forums

Serial Pinouts
''' 1 -> +3.3v 2 -> Tx 3 -> Rx 4 -> GND '''