That's the regular choice. But my phone has voice mail enabled, if I don't answer quickly enough, it directs the call to voice mail and stops ringing. And calling repeatedly is not fun; also it drains lot of power from N900 battery to answer those calls (you know). I don't want to be situation, where I use all juices from my lost N900 battery... that's why "a quick beep in every 30 secs for next 15 minutes" feature would be nice.

...and why not with a message in screen: "I have lost this phone, please call +555-123456. Reward!"