Sim card/network recognition

[InfiltratorSF]

My sim card worked fine but suddenly it stopped working for some reason, the network bars are there but I can do emergency calls only. When I try to register to the network it says "Unable to register. Try later". 24 hours later, same problem. I tried the various 2G/3G options but no avail.

Is this something with the sim card or a problem with the phone?

Thanks.