I finally got it working so I can IRC on my Prizm, so I guess you might want a tutorial.

Ingredients:
1 TTL to serial converter (An Arduino with the Atmega328 chip removed will do, that's what I use)
3 wires
1 2.5mm male stereo jack
1 VT100 emulator for Prizm
1 UNIX-based machine

Steps:

1. Plug your Prizm to your TTL converter (in my case an Arduino) using this schematic:
  (_)  tip
  |_|  ring
 _|_|_ sleeve
 -----
 _|_|_ -> to pin 0 (RX)
 _|_|_ -> to pin 1 (TX)
  | |
  |o|  -> to ground (GND)
 [___]
Then on your computer, you should have a serial port, in my case /dev/ttyACM0. If you use Windows, you can redirect COM1 to a Linux virtual machine.

2. Start up FXTerm on the Prizm at 38400 bauds, 8 data bits no parity 1 stop bit.

2.9. (Optional) You might want to change your password to a shorter one if it timeouts before you finished typing it on your prizm. Use passwd.

3. On the computer side, start agetty on the serial port (depends of your distro):

Arch Linux: sudo systemctl start getty@ttyACM0
Others: sudo agetty /dev/ttyACM0 38400 vt100
There you go, you should see a login prompt on your calc. Type in your username and password, then adjust the tty settings:
stty rows 36 columns 96 # 4x6
stty rows 36 columns 76 # 5x6
stty rows 27 columns 64 # 6x8
stty rows 27 columns 48 # 8x8
Then you can easily get on IRC using irssi. But I warn you, some of the control codes aren't implemented yet so it will look kinda ugly and you'll have refresh problems.

Have fun ^_^

so i would need to buy a serial jack to do this? I have the arduino, prizm, and vt100 term.

This is pretty much everything you need to get started. Plus a computer.

(The 2nd pic is whatever I tried to picture in the 1st step in the OP. And note that I removed the main chip of the Arduino so a direct connection is made from the Atmega8 (the USB part) to the pins 0 and 1 so it acts as a TTL-to-serial converter.)

They sell the 2.5mm thing at The Source and I got 10ft of wire like this at Home Hardware. I don't have any solder gun, but it might be a good idea if you don't want to hold the wires on the jack all the time.

They sell the 2.5mm thing at The Source and I got 10ft of wire like this at Home Hardware. I don't have any solder gun, but it might be a good idea if you don't want to hold the wires on the jack all the time.

Ok cool thanks for the info.

Also could you post pictures of the IRC in action? (if possible in such circumstances)

I finally got it working so I can IRC on my Prizm, so I guess you might want a tutorial.
...
Have fun ^_^

Nice use of fxTerm :-)
It should work also with fx9860G, I released fxTerm for 9860G some time ago here: http://ourl.ca/11749/332361
I am not sure if anybody tested it, so this could be a opportunity.