1.  Ubuntu 10.10 iPhone Toolchain 4
    If you use Ubuntu 11.04, please see wiki on how to use gcc-4.4 to compile

2.  Install the following packages in Ubuntu

    sudo apt-get update
    sudo apt-get install bison flex build-essential wget patch
    sudo apt-get install git autoconf gawk libssl-dev libxml2-dev uuid-dev
    sudo apt-get install clang

3.  Clone Project
    cd /
    sudo git clone git://github.com/javacom/toolchain4.git
    sudo chown -R <yourusername>:<yourusername> /toolchain4

4.  Put iPhoneOS4.2.sdk.tgz to /toolchain4/sdks/
    
    or build xar
    sudo apt-get install libxml2-dev
    ./toolchain.sh xar
    then put iPhoneSDK4_2.pkg to /toolchain4/sdks/
    ./toolchain.sh buildsys
    to build sys

    Put iPhoneSDK4_3.pkg to /toolchain4/sdks/
    ./toolchain.sh buildsys43
    to build sys43 folder

    Put iPhoneSDKHeadersAndLibs.pkg to /toolchain4/sdks/
    ./toolchain.sh build313
    to build sys313 folder

    Put iPhoneSDKHeadersAndLibs_32.pkg to /toolchain4/sdks/
    ./toolchain.sh build32
    to build sys32 folder

5.  Build headers tools and gcc 
    cd /toolchain4
    ./toolchain.sh buildsys
    ./toolchain.sh cctools
    ./toolchain.sh llvmgcc
    ./toolchain.sh ldid

6.  Install as_driver
    cd /toolchain4/as_driver
    make
    cd /usr/bin
    sudo mv as i686-linux-gnu-as
    sudo cp -p /toolchain4/as_driver/as_driver as
    sudo ln -s /toolchain4/pre/bin/arm-apple-darwin9-as .
    sudo mv ld i686-linux-gnu-ld
    sudo cp -p /toolchain4/as_driver/as_driver ld
    sudo ln -s /toolchain4/pre/bin/arm-apple-darwin9-ld .

7.  Test iOS4 sample code
    cd /toolchain4/Projects/LocalPush
    make
    make dist
    (LocalPush.app & LocalPush.ipa will be in build/4.0/ folder)

8.  Checkout the updated UICatalog in svn here
    sudo apt-get install subversion
    cd /toolchain4/Projects
    svn checkout http://apiexplorer.googlecode.com/svn/trunk/UICatalog UICatalog-read-only
    cd UICatalog-read-only 
    make -f Makefile.ios4 
    make -f Makefile.ios4 dist
    (Then install the build/4.0/UICatalog.ipa to iPhone for testing)

Enjoy.