It depends on the carrier. Some of them can take up to 24 hours to fully set up. (And it's not a hard and fast thing - you can activate 2 of the same model phone on the same plan with the same carrier. One can be fully activated n 2 minutes, the other can take 2 days.)
Give it at least 24 hours. Then call tech support if it's not working. Ask them to check that your account is properly provisioned. (If it's Straight Talk/Net 10, try their Facebook page - that's where their best techs are.)