Baseband Device

This is the device in the iPhone that manages all the functions which require an antenna. The baseband processor has its own RAM and firmware in NOR flash, separate from the ARM core resources. The baseband is a resource to the OS. The Wi-Fi and Bluetooth are managed by the main CPU, although the baseband stores their MAC addresses in its NVRAM.

The iPhone's baseband processor is the S-Gold 2. The iPhone 3G, the iPhone 3GS and the iPad make use of the X-Gold 608 chip for this purpose. The iPhone 4 (GSM) and iPad 2 (GSM) use the XMM 6180, while the iPhone 4 (CDMA) uses the MDM6600 and the iPhone 4S uses the MDM6610

You can check some Baseband Commands.

Seczone
This is the area in the baseband where the lock state is stored.

Layout
0x400--NCK token 0xA00--IMEI signature 0xB00--IMEI 0xC00--Locks table

Encryption
Many of the sections are encrypted using TEA based off the CHIPID and NORID. See NCK Brute Force for more info.

Exploits

 * SIM hacks

S-Gold 2

 * Fakeblank
 * IPSF
 * Minus 0x400
 * Minus 0x20000 with Back Extend Erase

X-Gold 608

 * JerrySIM
 * AT+stkprof
 * AT+XLOG Vulnerability
 * AT+XEMN Heap Overflow
 * AT+XAPP Vulnerability

XMM 6180

 * AT+XAPP Vulnerability

MDM6600

 * none right now

MDM6610

 * none right now

Theoretical Attacks

 * NCK Brute Force
 * Baseband JTAG

Boot Chain
bootrom->bootloader->firmware