FYI, when I register to my SIM's home network I get:
​cellular: csd[803]: ISI_SMS .584106> ind_reg_status(): Net registration (ind) status:1 rc:0

However when I try to register to a network to which I'm not allowed to roam I get what you were seeing yesterday:
cellular: csd[803]: ISI_SMS .670837> ind_reg_status(): Net registration (ind) status:0 rc:4

I think you should take this up with your carrier again.