Boot Output from the Ceiva2 shows that it runs VxWorks. So far I haven't been able to get anything from the prompt but a remote-echo, and the fact that ^X reboots the ceiva.

Documentation about the chips which I managed to find:
0418-00-BlueCat_31_Users_Guide.pdf
0421-01-BCL_31_TSG_7212.pdf
Hynix 64Mbit Synchronous DRAM
Intel StrataFlash 64Mbit Flash Memory
ISSI 16Mbit DRAM
Philips Hex Inverting Schmitt-trigger with 5v tolerant input.
CeivaManual_1a.pdf
CeivaManual_2a.pdf
Arm 922T Technical Reference Manual
Cirrus Logic EP7312 Development Kit Product Bulletin
Philips Embedded USB (2.0) Host Controller - ISP1160
Intel Advanced Boot Block Flash Memory
Silicon Labs ISOModem with Integrated Global DAA
Cirrus Logic EP7212 Arm720T SOC Data Sheet
LH7A400 Block Diagram
Metrowerks Board Support Package for LH7A400 EVB
Sharp LH7A400 SOC User's Guide
Epson RAMDAC LCD/CRT Controller Tech Manual
Shoehorn Bootloader Tarball
Silicon Labs ISOModem with Integrated Global DAA
Sharp LH7A400 SOC Preliminary Data Sheet

Images of the Ceiva 2 hardware:
Rear of the main logic board
Rear of the LCD backlight power board and part of main logic board
Modem Section
Connectors and USB area
Backlight Inverter Board
CPU and Memory area
USB and Memory Areas
CPU and Memory again
Overview of both boards
Back of both boards
LCD Label
Connection to LCD and LCD Board Edge
And closeups of the chips:

Info on putting Linux on the original Ceiva