Get root or re-install the OS without a USB cable? Usually, the guides for getting root or re-installing the OS on an Android device (I have a Samsung Galaxy S, which I'm mostly inetersted about) tell to flash the device from another computer through the USB cable.

Is it in principle possible to perform such modifications without using the USB cable (and another computer)?

Perhaps, by putting a file with the other version of the kernel/OS soemwhere on the device, and booting it in a special mode?

Imaginne the situation: I took the Samsung Galaxy S (and a laptop), but no USB cables, and went away from the civilization. Now it turns out that to use some of the apps I would like to use (like SSH server frontends for Android) I 


either have to re-install the Android OS (because they want a newer version; so I'd use CyanogenMod or Replicant because there are no offical upgrades from Samsung)
or have root (because they don't want to work without root).


Can this be done without a USB cable? 


(Of course, there is another good solution in this situation: take the source code of those apps, and fix them so that they will work for me, re-compile and install them.)


(AFAIU, after I have full (root) access to the device, I can re-install the OS without a cable and another computer: for example, I have another device that was supposed to work under Android -- Toshiba AC100, but after I installed Ubuntu 12.04 on it by flashing the device, I must be able to re-install the kernel from inside the OS -- there is a "flash-kernel" utility in Ubuntu.)
Use ROM Manager app. It can install ROMs from SD card. You can download your favorite ROMs using it, too.

And, Samsung Galaxy S is officially supported by it.