Many people don't know what is difference between Rooting, SIM unlocking and Bootloader Unlocking. Lets have a look.
Rooting an Android phone is simply adding a file to the system that allows
other apps to elevate their permissions and read, write, and execute
anything on your device. In this case, anything means anything -- if it
is user editable or actionable, you can do it with root. This is both
powerful and dangerous, so be sure to get all the answers and be clear
on the subject before you do it.
SIM or Network Unlocking
This allows a phone bought
for use on a particular network to be used on another network. If you
buy a phone designed to only work on Orange (or AT&T for an American
example), to use it on any other network, you will need to unlock the SIM programming.
This is what Justiceanthony has done in the example above, as he wants
to use an O2 phone on his carrier in Ghana. It's done without rooting or
modifying any firmware in your phone or tablet.
Remember, the networks have to be compatible. A phone with radios
designed for one carrier may not provide 3G or 4G service on another,
and sometimes they won't work at all.
All Android devices ship with a locked bootloader.
Some are very easy to unlock, like Nexus devices, some need a little
hacking to unlock (like most Samsung devices), and some are encrypted
and designed to be very difficult to unlock (hello, Moto). Bootloader
unlocking allows you to flash (write to your phone's "hard drive") image
files that haven't been signed with the official key from the folks who
made your phone or tablet.
A locked bootloader can flash a new recovery
provided in an OTA update because the recovery was signed with the
right key. It will fail to flash a custom recovery like ClockWorkMod. An
unlocked bootloader will flash anything that fits, as long as you tell
it to. Once a custom recovery (or sometimes a "Super" boot image) is
flashed, you can install and erase custom built system firmware at will.
Again, this means you need to do your homework before you start
fiddling with things.