Can we upgrade AT&T SAMSUNG-SGH-I897 Galaxy S to Android 4.1? I have the AT&amp;T Samsung Android Mobile with 2.3.5 OS and it's model no is SGH-I897. Now I want to upgrade my mobile os to lates 4.1 or 4.2, So can any body help me how to do that. Thanks in Advance.
Can we? Yes (But you have to go for a custom ROM)

How?
Well, you can use a custom ROM like CyanogenMod or better, you can use Salty Bean ROM.

Steps:


Backup everything. (including messages, contacts, apps, settings and OS)
Download the ROM
After downloading ROM package &amp; Salty Bean addons, connect your phone to the PC. Enable mass storage mode to access SD card data. Transfer both the files on it.
Disconnect the phone from computer. Now boot into the recovery mode. For doing the same, switch off the phone completely (until it vibrates). Press &amp; hold Volume Up + Volume Down + Power Key together until recovery mode appears (you can release power button after         Samsung logo appears but keep holding other two until recovery mode shows up).
After getting into the recovery mode, take a nandroid backup of your current ROM so that it can be restored back in case if anything goes wrong. To backup your current ROM, select Backup and Restore option from the recovery menu &amp; on next screen, select backup. Now It will make a nandroid backup of your whole system (excluding SD card).
Select wipe data/factory reset &amp; wipe cache partition to wipe all the data &amp; caches from the phone memory respectively.
Now Select install zip from sdcard &amp; then choose zip from sdcard. Select the ROM file from the location where you’ve transferred it earlier &amp; press on Yes to confirm the installation.


All the detailed information can be found here

If your are not sure of what to do, please do not attempt to do this. Get help from someone (as in getting help from someone who can hand your phone over to) instead