If you use Verizon as your cellular Internet provider and you are going to install and use the AT&T Global Dialer on your computer you may run into some issues. Typically users who have Verizon Access Manager (VZAccess) installed cannot install AT&T Global and get it working - it will stop installing then roll back the install. In some cases it also prevents VZAccess from functioning properly even though it was removed.
This has to do with the way AT&T Global Dialer inserts itself in the network stack - their process is messy and dangerous to put it nicely.
So you've installed AT&T and now VZAccess doesn't work? Uninstall AT&T Global if it managed to install, uninstall VZAccess, then restore your system to a point prior to the installation of AT&T' Global. Once the system restore is finished you may reinstall VZAccess and it whould work.
So you can't live without AT&T Global? You will need to download the installation app, but don't install it yet. Uninstall VZAccess, reboot, THEN install AT&T. Once AT&T is safely installed and your system has been rebooted you may then install VZAccess.
Do not taunt AT&T Global Dialer.