A. I had this exact problem. There are a few steps in getting your AT&T card working with your 64-bit OS.
First, download the latest version of the AT&T Communication Manager, shown here, from AT&T's site. Install Communication Manager and reboot.
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If your card still doesn't work and you're using a USB card, such as the Mercury I had, the next step is to make sure the correct 64-bit driver is being used instead of the 32-bit driver. Go to the folder C:\Program Files (x86)\Sierra Wireless Inc\TRU-Install\Drivers and copy swmsflt64.sys to the clipboard.
Now go to C:\Windows\SysWOW64\drivers and rename the existing swmsflt.sys to swmsflt.sys_old. Paste the symsflt64.sys we copied to the clipboard and then rename it to swmsflt.sys. You're essentially replacing the swmsflt.sys in the C:\Windows\sysWOW64\drivers folder with the 64-bit file provided with the AT&T Communications Manager. Repeat these steps to replace the 32-bit swmsflt.sys file to C:\Windows\System32\drivers.
Disconnect the device and reboot the computer. Once the reboot is complete, reattach the device and launch Communication Manager. The device should now work.
An alternative approach is to go directly to Sierra Wireless, the company that manufactures AirCards. Sierra has an enhanced version of 3G Watcher, an application created as a native wireless management application for their products, which has native Windows 7 32-bit and 64-bit drivers. Visit Sierra's site and select the AT&T carrier and type of device and a link to the latest build of 3G Watcher will be shown.Related Reading: