Its impossible to browse internett through the iPhone's browser

if "SAFARI" isnt working, try turning the phone off and on, try rebooting, try restoring...if none work, may have to bring it to an apple store if one is available in the area

As mentioned, reboot.
But you should also provide more details of what "does not function" mean. Do you mean it opens but cannot get it to go anywhere...is is slow...does it open but close out on your (crash)? Etc. Hard to help when all you say is it doesn't work.

A reset/reboot is:

Go to Home Screen
Press and Hold Home Button
Keep holding and press and hold Lock Button
Keep holding Both
You will see Slide to Turn Off (Don't let go to slide, just keep holding)
The phone will turn off (in time, but screen will look like it has some white lines)
Keep Holding
When you see the Apple Logo, you can let go.

Turning off via the Slide to Turn off while good and fine to turn off, is more like the Sleep Mode on a computer. Thus any locked up issues in memory remain when you turn back on. A reboot as described is like doing a real Turn off and Turn On on a computer.

You may also wish to read this tread about reboots and odd application behavior.
http://discussions.apple.com/message.jspa?messageID=5851978#5851978

kjempebra wrote:
Rebooting is no solution!

Next option after Rebooting if that didn't work, is to do a Restore via iTunes. After that, then you call to have it looked at for a replacement.

did you restore the iphone from a backup, or did you set it up as a new iphone

try restoring it as a new phone, when you restore the iphone from a backup you could be restoring the problems that caused you to restore

We can't help you. To use a different browser, you had to hack the phone. It's possible your hack is responsible for the problems you are having with Safari.

As above no help on this forum for a hacked phone. It is against the terms and conditions.