According to several posts on the hackint0sh forum, the chipset that will support the 3G iPhone will be the PMB8878 or better known as the S-GOLD3H.
The current version of the iPhone is powered by the S-GOLD2 chipset, so we might have found the chip that will power the next iPhone.
But maybe apple is planning to use another chipset, we will not know this until final release !

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Some features of the new chipset include:

-HSDPA 7.2 Mbit /s (3G)
-Support of Camera’s up to 5Mpixel

And a whole lot of other features that you can find on the bottom of the post or here.

K e y A p p l i c a t i o n F e a t u r e s
?¦ ARM 926 based single modem and application processor with cache
support and fast tightly-coupled memories
?¦ Hardware Crypto box – DRM 2.0, SIM Lock, IMAI protection
?¦ Hardware security – E-fuse, Boot Code Protection, Secure Mode
?¦ CPU, RGB display interface supporting high resolution color displays
up to HVGA
?¦ High-speed serial display interface for cost effective clamshell
mechanics up to HVGA
?¦ Support of cameras up to 5 MPixel
?¦ MPEG4 / H.263 hardware accelerator
?¦ MP3, AAC, AAC+, enhanced AAC+
?¦ 2D Graphic hardware
?¦ Support for video telephony, streaming, recording and playback
?¦ 2 x MMC/SD interfaces, SDIO capable
?¦ USB 2.0 on-the-go, full speed
?¦ Fast IRDA
?¦ Multimedia extension interface (MMIC-IF) for support of high end
graphic accelerators
?¦ 2 bi-directional digital audio interfaces (I2S) to connect audio
companion ICs and Bluetooth modules
?¦ Dedicated NAND flash controller supporting burst mode and error
detection
?¦ Support of DDR-SDRAM devices

K e y M o d e m F e a t u r e s
?¦ HSDPA – category 8 (7.2 Mbit/s)
??“ Implementation of fractional chip rate
equalizer
??“ Configurable to lower categories / data rates
??“ Option to switch off HSDPA to save power
?¦ WCDMA
??“ 384 kbit/s class for uplink and downlink
??“ 640 kbit/s peak data rates for uplink and
downlink independently
?¦ EDGE multislot class 12
?¦ GPRS / GSM
?¦ FR, HR, EFR, AMR
?¦ SAIC
?¦ Tx diversity
?¦ DTM class 11
?¦ Polyphonic Ringer support for up to 64 voices at
up to 48 kHz sampling rate
?¦ Echo cancellation/noise reduction
?¦ GTT/TTY