are these calls all going to people who are members of an organization?
Perhaps you can divide the roster of numbers up and assign each to call between 2 and 5 people....the problem is that not everyone will follow through and all those on the list that do not get called will not receive the info. there is also such technology as a conference call, where every one is actually on the line at the same time...I have heard this done with businesses and for work training info that needs to be heard by all co-workers...when composing the information to be sent it would be best to use the guidelines for press releases: include the basic info--who, what, where, when as clearly as possible. (remember the game of telephone...that info can morph and change as it passes along)

this is what it says here:
http://www.wisegeek.com/what-is-a-phone-tree.htm

Generally, a phone tree is organized by a single person, to eliminate confusion. The person organizing the phone tree collects information about all of the individuals who should be included in the phone tree. For example, a small rural school might have a phone tree which could be used to notify people about canceled school days and other events of relevance to the school.

Ideally, the organizer would collect at least two contact numbers for each person, including a contact number with an answering machine or voicemail. Once the list of people is collected, it can be divided up to create an organized phone tree, which is copied and given to all members of the group. Because the people at the top of the phone tree are crucial, it is a good idea to pick the most reliable members of the group for these positions, ensuring that information will be passed on.

most phones allow a multi-call feature where one person can get several onthers on the line (usually by dialing * or #)

you might also consider a conference call..
http://en.wikipedia.org/wiki/Conference_call

http://www.powwownow.com/ has some info and programs to do this with
land lines and cell phones..

there was an early chat feature for on-line communications called Powwow which was a start up company stemming from the McAfee virus protection company folks. I do not know if this is related. (or even if this program is still available...http://powwow.jazy.net/
http://en.wikipedia.org/wiki/PowWow_%28chat_program%29)
http://jazy.net/content/rest-peace-powwow-chat
I guess this "Tribal Voice" program no longer is current...