Wow, that's funny about the "magic age" of 3 yrs 3 months -that's exactly the age my ds was! We had been practicing sitting on the potty for a year, sometimes trying more than others. In the end - we bought underwear, told him about it, that when he learns, he'll get to use big-boy underwear. Nothing happened differently. So on a long weekend (MLK day weekend) I said "This weekend we're going to try on your underwear!". So we did, he had a few "accidents" the first day - just learning/remembering to use the potty instead of his pants. That was it - no accidents since. A few weeks later we did underwear at night with no problem -ds asked for underwear at night.
So, take a little more time. Good luck!