Using EM7455 with AT&T SIM card in Asia

Hi, I have a EM7455 module with a US AT&T SIM card in Asia. The local carrier here is Far EasTone.

I am using the AT^SYSCONFIG command to enable and disable ROAMING. The strange thing is that when I turn OFF roaming, the module can still connect to the network. I even reset the module, and it still can connect to the network. Shouldn’t it not be able to connect to the network after I turn off roaming?

Also another question: do I need to reset the module after using the AT^SYSCONFIG command to enable/disable roaming? Or does it take effect right away without having to do a module reset?