A little update, concerning people who cannot use it on v04.39:

It does not work on all handsets, it mostly works on firmware releases with major revision 4.xx, but in some phones with "operator modified" v03.xx it works too. And it seems not to work in some other v04.39 handsets. Unfortunately, if the program detects you that «your phone doesn't support this mode», it will tell you so, and there's nothing you can do about it :-(

sorry about this