This manufacturer also produces other models.
These devices are end-of-life at GrandStream; their replacements use BT200 boards which are RoHS compliant and have more memory.
DSP system-on-chip: TMS320VC5402, with an extensive user manual. The PGE100 version is green, in that it is RoHS-compliant and uses no Pb/Br.
A second (important?) chip mysteriously hidden under paint. The most likely candidate is the same one as found in the GXP-2020 model: A coprocessor 320AIC20K from Texas Instruments interfaces speaker, microphone and line in/out to the DSP over I2C or S2C. It includes support for oversampling and filtering.
Flash memory: 512k x 16, or 1024k x 8: MX29LV800BBTC-70. The cycle speed is 70 ns, making this flash suitable for running code directly. This means that smaller RAM will do.
Static RAM: 128k x 16, or 256k x 8: IS61LV12816-107.
JP2 connects to I/O peripherals: speaker, LCD, keyboard, LEDs. The peripherals are the same as used for BT200 boards.
The JTAG/bootloader connector used in these Grandstream phones is a 16-pin connector. Its solder islands are open on the PCB, so soldering in a 0.1" pitched two-row pin header is easy.