See if your friend created a backup of your phone - that's a suggested step in lots of root instructions, and it is possible he did this so you can just re-add the missing application.
Assuming this wasn't done though, you may want to just start over. The following webpage has information on using ODIN (Samsung service application) to restore the original software to your phone. It looks like it covers all the regional variants, you'll need to read carefully to find the applicable software and process for your region. If you provide more regional information, I'll see if I can find more precise steps.
I don't speak the language and the Google translate is very sloppy - so I may be misunderstanding this thread. Hopefully you speak the language.
For a Brazilian phone, this forum thread has steps for installing a rooted stock 2.3.4 update (sounds like a prerelease leak of an official ROM, which are common to Samsung devices) and reply #8 in the thread also gives steps for installing the 2.2 version that you have installed right now.
Since I started replying, that forum stopped responding. Hopefully just a temporary glitch, but just in case, here's another page I found that includes links to download the Brazilian software.