[AT&T Samsung Galaxy S II SGH-I777] atinm:
CyanogenMod is a free, community built, aftermarket firmware distribution of Android 4.0 (ICS), which is designed to increase performance and reliability over stock Android for your device.

#include <std_disclaimer.h>
/*
* Your warranty is now void.
*
* I am not responsible for bricked devices, dead SD cards,
* thermonuclear war, or you getting fired because the alarm app failed. Please
* do some research if you have any concerns about features included in this ROM
* before flashing it! YOU are choosing to make these modifications, and if
* you point the finger at me for messing up your device, I will laugh at you.
*
* Submitting bug reports on nightly builds is the leading
* cause of male impotence.
*/

CyanogenMod is based on the Android Open Source Project with extra contributions from many people within the Android community. It can be used without any need to have any Google application installed. Linked below is a package that has come from another Android project that restore the Google parts. CyanogenMod does still include various hardware-specific code, which is also slowly being open-sourced anyway.

All the source code for CyanogenMod is available in the CyanogenMod Github repo. And if you would like to contribute to CyanogenMod, please visit out Gerrit Code Review. You can also view the Changelog for a full list of changes & features.

http://teamhacksung.org/wiki/index.php/CyanogenMod9:GT-I9100:Nightly:Known_issues (All the same issues as GT-I9100 as almost all the code is the same - so pointing to the GT-I9100)

THE CM-TEAM DOESN'T ACCEPT BUG REPORTS OR FEATURE REQUESTS ON NIGHTLY BUILDS!

A MISSING FEATURE IS NOT A BUG!!!

FAQs: Same as the GT-I9100 -- essentially the same code.

FAQs: http://teamhacksung.org/wiki/index.php/Experimental:GT-I9100:Frequently_Asked_Questions

SPECIAL XDA NOOB FAQs: http://teamhacksung.org/wiki/index.php/Experimental:GT-I9100:XDA_Asked_Questions

First time installing CyanogenMod 9 to your AT&T Galaxy S II (SGH-I777), or coming from another ROM:

- READ FAQs: http://teamhacksung.org/wiki/index.php/Experimental:GT-I9100:Frequently_Asked_Questions

- Make sure you're running SGH-I777 bootloaders only (only the ones that are specifically released for the SGH-I777 -- official Gingerbread bootloaders work fine!) and a proper working CWM like the one from CM7

- Copy GApps and CM9 ZIPs to your internal SDCard

- Boot into Recovery

- Flash CM9 zip

- Flash GApps zip

- DO A DATA WIPE / FACTORY RESET (otherwise your calendar sync will not work)

- Reboot

- Don't restore Apps using Titanium Backup!

Upgrading from earlier version of CyanogenMod 9:

- Copy CM9 ZIP to your internal SDCard

- Boot into Recovery

- Flash CM9 zip

- Wipe cache partition and dalvik-cache

- Reboot

STOP!!!

Did you read THIS POST fully, the FAQs and KNOWN ISSUES?

No

DO IT or leave this thread immediately.

If you download anyway and start asking already answered or dumb questions, you'll get flamed.

This is fully YOUR OWN FAULT then!

Yes

Here's the download link for you.

Nightly builds can be found at ROM-Manager or at:

http://download.cyanogenmod.com/?device=i777

Google Apps:

Get the latest Version from: http://goo-inside.me/gapps

CWM flashable Modems:

UCLC2

UCKK6

UCKJ4

UCKH7

Changelogs:

http://cm-nightlies.appspot.com/?device=i777

http://cm-nightlies.appspot.com/?device=galaxys2 -- mostly shared by the i777

Webchat: http://webchat.freenode.net/?randomnick=1&channels=teamhacksung-support&uio=d4

Server: chat.freenode.net

Channel: #teamhacksung-support

Don't expect any support if you:

- are not running stock cm-kernel

- have installed any mods

- have modified system files

Thread for Developers only(!!!):

http://xdaforums.com/showthread.php?t=1568852

AdamG-, atinm, codeworkx, coolya, Entropy512, guiper, nebkat, Unhelpful, xplodwild, teamhacksung, the cyanogenmod-team.