Emergency calls only? That's because you don't have a cellphone account. IOW, you can't use the phone. All cellphones, with or without accounts, are required to be able to make emergency calls. But we can't say exactly why yours isn't registering on the network as a registered phone.
You DID follow the instructions and register the phone, right? And waited at least a few hours before posting the problem?
If it still doesn't register, go to Straight Talk's FB and ask for help. That's where their customer service people are.