Some more new info since yesterday, July 17, about the problem of the Futurama voice cast.

Don't forget that 20th Century Fox TV is the production studio of Futurama, and that is not FOX Network. HITFLIX.com, is clarifying that "[..] they are not the same thing and they have completely different corporate structures and a deal with one is not a deal with the other".

Talking about salaries of the voice cast, Variety.com says that: "It's believed that the Futurama cast members were asking for around $75,000 per episode; it was not clear what 20th (Century Fox TV) was offering. Calls to the voice stars' reps were not immediately returned."
This is insane because the Simpsons voice cast get paid around $400,000 per episode, that means that the Futurama cast is asking the 19% of the salary of the Simpsons cast per regular character (that's my guess).

I've also read that people are trying to contact the Futurama voice cast agents and producers Matt Groening and David X Cohen, but there's no luck yet, except for the statements of Phil LaMarr (Hermes) at his Facebook page:

The question that emerges right now is: What will happen to the San Diego Comic Con 2009 Futurama Panel?. The Guest are Billy West, Katey Sagal, John DiMaggio, Maurice LaMarche, Matt Groening & David Cohen, and they are supposed to appear on Saturday, July 25.

UPDATE 1: I've added the (supposed) "Press Release for the recast of the Futurama voices" at the Futurama returns! news section.

Sources: HITFLIX.com, Variety.com, Facebook.com