(1) There are services that you can set up where you talk to someone on a scheduled number, its called conference calling. Businesses use this all the time. Set up a schedule, pay in advance, people call in to the same number, you talk. The service cannot effectively track where you are calling from - heck, you can be using voice over IP - dial up to an ISP, then call the conference call and talk into your laptop.
(2) These same services also provide a "forwarding" feature where you call a number, and it "reroutes" the call through their number to the destination - preventing a trace!. See this service (a few paragraphs down the page): Connected Call Transfers. Visualize calling from a pay phone on a disposable phone card, to the connected call transfer service, to the conference call. Yeah, the LEOs are going to track that really quick.
Phone phreaks (yeah, that's how they spelled it) can actually route a call around the world a half dozen times through multiple exchanges - for free. These guys could do that. So - tracing the call is likely to be unproductive if these guys have the right skills and knowledge. But - I think the message that the Moose gave fits perfectly for a conference call.