http://m.pocketnow.com/tweaks-hacks/motorola-atrix-4g-how-to-change-wi-fi-and-bt-mac
All procedures were done under Defy CM7 rom. Spoof at your own risk.
1.Find out your original MAC address and write it down.
2.Download and install HexEditor from Market.
3.Backup /pds/wifi/nvs_map.bin.
4.Open /pds/wifi/nvs_map.bin in HexEditor.
5.You will see your original MAC address in reverse way at address 00000003-00000006 and 0000000a-0000000b
for example if ur original MAC is 98:4b:35:49:f6:a5 you will see as the image below.
6.Put the MAC address you want at these places also in reverse way.
7.Save and reboot.