Don't forget we also have the USB lines, which might eventually be more interesting than the 3 pin serial port - even if each pin of the 2.5 mm jack can only be used for its original purpose (i.e. not like on the TI calcs), a network where TX is through the USB and RX is through the 3 pin port can still be possible, assuming we figure out how to control at least one of the USB lines. If we learn to control two lines on the USB, then we can forget about the 3 pin port (or use it for other purposes while keeping network connection on the USB).

IIRC there was someone hacking around the USB, what were the results?

And by the way, I know I can probably find this out reading some documentation, but what is the maximum baudrate achievable for the 3 pin serial port (I mean technically, not the one used in file transfer, unless file transfer uses the maximum)?.

Prizm - 460800 bps (used in cgPlayer), I didn't find a way how to set more.
fx9860G - 1.8 Mbps (used in fxPlayer), but it seems it is not a limit.

What? The fx9860G can be set up to be almost as fast as my internet connection?

Well, I asked about the baudrate because I always found 3-pin file transfers to be a slow. I thought it could be a great idea to develop an alternative file transfer software.
For those with a fx9860G with SD card slot, it's even more interesting, since the SD card can store very large files which are certainly a pain to transfer using the original function for that. Using the full 1.8 Mbps speed, it should be much faster (225 KB/s, woot! ), unless the access to the card is not fast enough to handle these speeds.

Other than that, I have lots of ideas for network programs (I even thought of some awesomely looking network chat, for the Prizm, with colors), but since there isn't anything like calcnet for the Casios yet...

I'm still investigating the serial port, and trying to map it to the different possible models that we could be dealing with, as you can see in the Casio Prizm Documentation thread. I really hope we're dealing with a 7720-compatible model, because that would mean I can turn both serial lines to bidirectional. If it's a 7730, I can only turn TxD into a receive line, giving us two receive lines, but the RxD remains unidirectional. The worst case is a 7705-type SIOF module, like the fx9860, because that has two unidirectional lines, end of story.

Chances are that it's a standard UART controller, which generally allows a serial mode and a raw mode (which is what we'd want).

Wow, this is really interesting! Allowing casios to communicate with TI-calcs would eb really awesome!

As it is, I could write a TI calculator program that would make them speak the same protocol as the Casio calculators, but that would only give us one-to-one communications. CALCnet networks of Casio and TI calculators together would of course be amazing.

A Casio and a TI together would be amazing. I can just imagine Obliterate.

Actually, making them play nicely together game-wise, especially with the different screen resolutions and such, might be quite the interesting challenge.