New lines are a bit like new website domains. They may take 24 to 48 hours (possibly longer in odd cases) before various other phone services "see" them or know about them. It comes down to when is the number completely added to routing tables, etc. The new number can likely call out almost immediately. But incoming calls may not be routed from various services at the same time. So a call from Verizon may start working a few hours before (or after) calls from VOIPo or whomever.