There is a free gatekeeper available. You just need the files on a e-mail format and unzip them on your P.C. It will do the gatekeeping for any H323 phones or devices.
Go to http://www.gnugk.org/. Download only the files needed for the window aplications.
Do not get scared by all the tech. terms. If you do not want to work on the programing, like most of the users, you just load it into your machine and it works. You do not need to know how it works to install it into a P.C. and get it to work in about 10 minutes.