Can you give more details? Are you a new customer? Did you order a replacement sim? 

I'm a new customer; I just got the SIM card. insert into the phone, but no network. SOS only. I tried it on another phone, but it didn't work either.

SIM cards should come pre-activated. It looks like your didn’t. Have you had the chance to create a self-serve account?  

Thanks! I believed that the SIM that I received did not pre-activated. Luckily, my friend has a backup SIM card. I changed to that card and used Self Serve → Mobile services → Change your SIM number and it is fine now. Thanks!