Atrix 4G Tethering Conf

Menu > Setting > Wireless & network > Mobile networks
> Access point names > Menu > New APN >

Name:      AT&T
APN:       wap.cingular
Port:      80
Username:  WAP@CINGULARGPRS.COM
Password:  CINGULAR1
MMSC:      http://mmsc.cingular.com
MMS proxy: wireless.cingular.com
MMS port:  80
MCC:       310
MNC:       410

Menu > Save

Home > Menu > Settings > Wireless & network > Mobile networks
> Access point names > AT&T

Home > Menu > Settings > Wireless & network > Mobile hotspot > Wi-Fi hotspot
Home > Menu > Settings > Wireless & network > Mobile hotspot
> Wi-Fi hotspot settings > Configure Wi-Fi hotspot > [enter SSID] > Save

Confirm RED icon at the top turn to BLUE.

ref: MobileTechVideos