The custom conferencing web gui should be based around the latest version of the open source PBX; Asterisk and easily integrated into a package like Trixbox. The functionality requirements will be very similar to web meetme. It will need to be written in PHP/MySQL with supporting controls. Keep in mind that the scheduler for webmeetme4 is probably written in C. Webmeetme4 will be a good starting point. Functionality will consist of multiple tier auth system (admin and user), scheduling and user call back functions. This will need to be part of the deliverable as well.
Rent A Coder requirements notice: As originally posted, this bid request does not have complete details. Should a dispute arise and this project go into arbitration "as is", the contract's vagueness might cause it to be interpreted against you, even though you were acting in good-faith. So for your protection, if you are interested in this project, please work-out and document the requirements onsite.
The application should be modeled after the existing open source project - web meetme. This web application will, at a minimum, need to have all of the same features and functionality as the web meetme application with the addition of a callback function, which we have outlined specifications for.
We have in house coders to do this, but time is short at the moment.