Hey guys, heres a guide on how to convert(NOT PORT) roms from the i9100 to the i777, why not port you say? well simple really, these two devices are almost mirrors of each other, and so the aspect of 'porting" doesn't apply here, as the term "porting" in android is meant mostly when your working on any given custom android framework to work on a device it wasn't meant for, for example making a full sense rom work on a samsung device or vice verse a touch wiz rom on an htc device, now that i have cleared that out of the way heres the steps you need to follow:
1.Download any given i9100 rom, also make sure you have a i777 stock/custom rom as you will need to grab files from it.
2.Open the i9100 rom zip you downloaded, then navigate to /system , once there delete the "usr" folder, after that open the stock/custom i777 rom zip and extract the "usr" folder inside "/system" to your desktop or any given directory inside your PC, then drag and drop the "usr" folder you extracted from the stock/custom i777 rom to your "/system" directory of your i9100 rom zip.
3.Now navigate to "/system/app" on your already opened i9100 rom zip and delete "FMradio.apk", after that go back to "/system" and open the file called "build.prop"(you can open it using Note++ ) here you need to change a few things, which are as follow:
ro.build.description=GT-I9100-user 2.3.6 GINGERBREAD XWKK5 release-keys
To their i777 counterparts, which are as follow:
ro.build.description=SGH-I777-user 2.3.6 GINGERBREAD UCKK6 release-keys
After your done close it, then winrar will ask you the following "file "xxxx" was modified, do you wish to update the archive" hit yes
4.Now we need to replace the kernel/modem.bin(if any) inside the already opened i9100 rom zip with i777 ones, here you can choose which ever modem.bin(i777/i9100), but for the kernel it has to be a one that works on stock sammy roms or sammy roms/aosp roms(like SiyahKernel v2.6.12).
5. Now on your already opened i9100 rom zip navigate to "\META-INF\com\google\android" and open the "updater-script" here you will need to delete any string pointing to i9100 like for example the following string:
assert(getprop("ro.product.device") == "i9100" ||
getprop("ro.build.product") == "i9100");
If you see these just select them and hit backspace, after that close it, then winrar will ask you the following "file "xxxx" was modified, do you wish to update the archive" hit yes
6.Close the already opened i9100 rom zip, after this you should have successfully converted the i9100 to work on your i777 without a hitch.
7. Now all there's left is to copy the modified i9100 rom and place it on the root directory of your internal/external sdcard(which ever you prefer) and flash it.
Note: Some people will wine about the explanation i gave about the differences between converting and porting, if your one of them i welcome you to discuss it here with me, also if you get lost in any of the steps just post your question here il do my best to help you out, and last but not least qualcomm S3 SGS2 users should also be able to benefit from this guide just use/edit the same files but use the ones from another qualcomm s3 sgsII device e.g Tmobile SGS2 files to use an Att Skyrocket rom.