Security settings on types of phone calls is on the roadmap, though I don't have a timeframe.
I have simulated requiring a PIN by creating a Number Plan with a Match Type of Regular Expression. Then, I add my PIN to the beginning of the Regular Expression for Match Data so that someone has to know to dial those digits first before dialing an International number. In the Normalized Format Data I strip those digits back off.
For example, 1234(0)?/d{10} for a 10-digit international dial with an optional leading 0.
Unfortunately, I then need to modify Outbound Dialing contact lists or anything else that needs to dial International calls to have the PIN included.