When I first got Roo, we hung a bell on the door and everytime I took him to potty I made him touch the bell with his paw. Within 2 weeks he was doing this on his own. This worked out great because Roo is quiet for the most part and when I was upstairs I could hear if he needed to go out. By 5 months he was 100% housebroken. When their young, the key is to make them go potty before they tell you.
I use bells with my B. He learned to use them in like 2 days. Since then, I've only had "accidents" when I ignore him b/c I'm busy. Sometimes he rings them just to go out to play, but other times he rings them when he REALLY has to pee. The best thing is, they are portable so when I go visiting with him he always knows how to tell me he has to pee.