Update
I contacted the suppor center and, i sent them a capture, they installed to me the "Manual Entry Disconnect Tone" pmf file configured with the 420@-10,420@-10;2(0.5/0.5/1+2) tone.
Still it doesn't disconnect so they said they will pass the issue to the 2nd level...
In the meanwhile if somebody had similar issue with italian provider Tiscali on PSTN, let me know
Stefano