Hi B., My son was 3 in July. I started a couple times before then, but he just wasn't ready mentally. Finally, one day I learned how important it was to him to be considered a "big boy" and not a baby. I explained to him that big boys don't wear pull ups or diapers. He of coarse wanted to wear the underwear, so when I would ask him to go try to go potty, if he fussed or argued I would just calmly say:"okay, then I guess I'll just have to put a diaper on you since babies wear them and babies go in their pants" He'd run to the potty every time to prove he's a big boy. Afterwards I'd give him a high five and remind him how much faster that was than mommy having to change a dirty pants. He still wears a pull up to bed at night. I'm not worried about that yet. I have family that had trouble with that growing up, so it might be genetics that his bladder is too relaxed during sleep to hold it. Anyway, I hope this helps. Like the other moms said, don't worry too much. It'll happen.
S.