DIY Conferencing with Asterisk
Some folks, in search of a cheap conferencing solution, consider the do it yourself option, leveraging the Asterisk open source PBX. This is a reasonably viable option for folks whose other alternative is a "bottom feeder" (see the conferencing howto for a more detailed description) or for those with full time IT specialists on staff.
There are two ways to implement this solution - with existing telco capacity (T1s or PRIs) or with VoIP connectivity. If you can leverage existing capacity, that's always a way to get more bang for your buck. If you're adding capacity, VoIP can be a very good solution.