iFixit

Big players on the front of the motherboard include:

• Samsung KB100L00WM-A453 4Gb (512 MB) of mobile DRAM which contains a 1 GHz Intrinsity Processor in a package-on-package configuration, according to the fine folks at Chipworks.
• ST Ericsson's THOR M5730 HSPA+ Thin Modem
• Bosch Sensortec Accelerometer
• Maxim MAX8987 DC Power Management
• ST Ericsson GNS7560 Single Chip GPS Solution

Here's an ultra high-res version of this image, in case you want to inspect the board thoroughly.

On the back of the board:

• Broadcom BCM4329 802.11n Wi-Fi, Bluetooth 2.1, and FM Tuner
• Wolfson Microelectronics WM8994 Audio CODEC
• Skyworks SKY77460 WCDMA/HSPA+ Power Amplifier
• ST Ericsson RF5000 Radio Transceiver (part of THOR M570 chipset)
• Skyworks SKY77544 TX-RX Front End Module
• Skyworks SKY77447 Load Insensitive Power Amplifier for WCDMA / HSDPA / HSUPA / HSPA+ Band II

An ultra high-res version of this picture can be seen here.

The headphone jack, earpiece speaker, and proximity/ambient light sensors reside on one cable.

Seems oddly familiar...

We applaud the efforts of smartphone manufacturers to move commonly-broken components (such as the headphone jack) to cables/boards separate from the motherboard. But attaching several components on the same cable also increases the overall cost of the cable, thereby increasing the repair cost of just one component.

Unfortunately, the Galaxy S 4G cannot be disassembled further without prying the front panel off the inner metal frame.

• Heat gun time!

Separating the front panel assembly from the rear panel assembly requires loosening the adhesive around the perimeter.

Add a little heat and some opposing forces, and BAM! Front panel and rear panel successfully separated.

On the back of the display assembly we find the Atmel mXT 224 touchscreen controller, which provides capacitive multi-touch capabilities, and is also found in yesterday's Motorola Atrix teardown.

The outer chromed plastic ring can now be removed from the metal inner frame.

At this point we can also remove the button capacitive touch sensors, vibrator unit, lower microphone, and antenna cable connector -- all of which lie on the same assembly.

Before we continue any further with the teardown, we have an experiment to conduct.

Ladies and gentlemen, welcome to the first ever segment of Science with iFixit.

Without any further ado, let's proceed!

Children (and adults, for that matter): DO NOT TRY THIS AT HOME. Failure to heed this warning could result in injuries such as finger burns. We are trained professionals.

Word on the street was that Samsung was using magnesium instead of aluminum for some of its structural components. The most obvious candidate was the main structural support plate that nearly every component on the phone mounted to. But how could we find out for sure?

A simple way to verify the magnesium hypothesis was to file away a small pile of dust from the mid-plane frame and...well...light it on fire.

• When you add a little heat in the presence of magnesium and the air we breathe, magnesium oxide and a little bit of magnesium nitride are formed. Byproducts of this reaction are very intense heat and extremely bright light.

Yup, looks like it's magnesium.

But why magnesium? If you take a look at your old pal, the Periodic Table, it is one of the lightest metals - more so than even aluminum. Additionally, its high strength makes it ideal for providing structural support where weight is a major concern.