I have found the thread to use my 7520 as a modem for my laptop.

I even found a specic question about Error 680 "No Dial Tone"

How do I review the over 500 responses?

http://blackberryforums.com/search.php?searchid=660121

I have the Blackberry Desk Top Manager running and everything loaded.

Thanks!

I would suggest that you delete the modem entry from your PC and uninstall the Desktop Manager. Reboot and then reinstall Desktop Manager (make sure the BB is not connected). Then follow the instructions in the thread you listed again. I had problems the first time I tried to setup my BB as a modem. After following the above steps I was able to configure the BB as a modem without any further problems.