Adds a second sound card to your PC (if you already have one).
Most VoIP software (like Skype or a Softphone) let you choose a different sound card for that application.
That means you may still be able to use the speakers on the PC normally, but use a handset or headset plugged into the USB Sound Card to make phone calls. In Windows, you'd need to go to Sounds and Audio Devices in the Control Panel, click on the Audio tab, and choose the systems main sound card for the system to use in general, in the drop-down box. Then go into your VoIP application, and choose the USB Sound Card for that application (only). Sometimes it will work, sometimes it will work right, and sometimes it won't. You do need to be a little geeky to mess with this stuff in Windows.
If you just need to use a handset temporarily to make a call, most PCs will simply change over to the USB Sound Card Dongle for all audio when you plug it in. That's handy if you're going to use Skype etc. on one or two calls on a desktop or laptop. It will let you use Skype etc. right away, and then usually return the system to using the built-in sound card, and then unplug it to return to the regular speakers (may require a reboot).
If you are using a handset in a kiosk, it's a better idea to plug directly into a sound card if it's available, rather than a USB device. On reboot, sometimes USB drivers don't load correctly in Windows.
The USB Sound Card Dongle uses Generic USB Audio drivers compatible with almost all modern PCs. It doesn't come with a driver disk, but it has worked with every semi-modern machine we've tried it on.
There are much more expensive USB sound cards out there, but this was the best we could find that worked perfectly, at a reasonable price.