Hi,

> No, if ofono don't request it and the modem can't send the response

I think you have no idea what you're talking about.  The 'spec' way of doing 
this is sending AT+CREG=2, at which point the modem will send a +CREG: 
unsolicited result code whenever the registration state changes (e.g. roaming, 
searching, home, etc).  See 27.007 Section 7.2.  

oFono also requests the registration status whenever any registration 
operation is performed.  This works, you can even test it on phonesim if you 
like.

>
> >> Suppose UI want to show the status, which interface can be used?
> >
> >You use the NetworkRegistration interface, 'Status' property.
>
> That's the point; the status can't be changed because ofono only get the
> status at modem/networking initialization, during registered to roaming
> ofono don't know the changing even modem update the information correctly

Again, you're wrong.  Take a look at ofono_network_registration_notify in 
src/network.c and and creg_notify in drivers/atmodem/network-registration.c.

I ask you again, are you sure your modem is actually switching its status, and 
if so, can you provide a debug trace?

Regards,
-Denis