- Leave the modem out of your machine's USB port
- Download this software from SierraWireless if you've previously installed SierraWireless software
- Run the "Watcher Remover"
- Restart your machine
- Open "System Preferences"
- Click the icon that's likely blank with a phone icon
- From the drop-down that likely says "Default", select "Add Configuration"
- Label it something like "ATT"
- Click "Advanced"
- Select "SierraWireless" from the "Vendor" list
- Select "GSM" from the "Model" list
- Click "Ok"
- Make sure you check the box that says "Show Modem Status in Menu Bar"
- Close your Preferences (you should now have the little phone icon on the upper right of your screen where the time is typically displayed)
- Insert the USB modem
- From the phone/modem icon in the upper right, select "Connect" (if the connection profile you just created is the only one you have, it will automatically have a check mark next to it; with multiple connections, make sure the connection profile is checked)
Enjoy.