>>> Method 1: Flight mode:

Put your phone in "Flight mode" with Psiloc System Tools. Install System Tools, open it and select "Flight mode". This way you can restart the phone without your SIM card so there will be no running phone tasks in the background. Now you can have up to 3,5 MB of free RAM!

Note: ironically enough, Flight mode doesn't work when Smart Launcher is installed, at least in my case.
But i've also heard several reports of people who have both apps running without any problems.

>>> Method 2: Smart Launcher trick:

Install Smart Launcher and open it. Go to Options, Settings and put Launcher ON.
Now plug in your charger and switch off your phone. Wait untill the battery meter appears and short press the Menu button (don't hold).
The menu should appear and now you can have 3,5 to 4,5 MB free RAM! (Hold Menu button to check RAM).

The trick is that with the charger plugged in, the phone must get a minimum software support for charging, even when
the phone is switched off. And somehow Smart Launcher has still got it's shortcut running and that's the Menu button. So when
you press the Menu button, you go directly to the Menu without any other phone tasks running in the background so
you trick the phone and you have more free RAM!
Note: when you unplug the charger, the phone will switch off.

>>> Method 3: Menu :

This method I found it by myself, it frees a little about 100~200 KB but I guess it's useful sometime

Close your menu not by selecting the right selection key "exit", or pressing the menu key another time, they only hide the menu app but do not close it, to close it select the left selection key "option" and scroll down and select "exit"

So when you open an app needs more ram reopen menu and close it, it's useful when play low bit rate video in realplayer paradis.