Could anyone give me some advice on setting up an Asterisk Telephone System, please?

So far, I have successfully installed the actual Elastix Asterisk software onto my small server.

I have got a SIP Trunk account from VoIP Unlimited and using our existing broadband connection via our EiS Broadband - Kent Service Public Network.

I think I have entered all details correctly, but it does not seem to be registered with the SIP Trunk account at VoIP Unlimited.

I have asked the technical team at EiS to open the UDP 5060 port and allow VoIP Unlimited server IP addresses range to pass through.

My internal IP address for the PBX Server is 10.57.24.50 and DNS is set to 127.0.0.1 and default gateway is 10.57.24.1

The communication between internal phone calls are connected successfully, but not outside.

Are there any other settings that I need to configure or consider both internally and externally?

Thank you very much for your suggestions in advance,

Supawat