Does anyone know a good place to check cell phone numbers?

Well, depending on where you live, you could go to all the different cell phone providers, here they each have their own phone number look up i believe.. And if not, try like 411.com ? i know they have a canada411.com here.. and that tells me numbers and reverse phone number look ups. Why not all it to find out whom it belongs to, and how'd you get the number ?