MNO will publish the Network ID in the DNS infrastructure so each mobile only need to resolve a simple DNS query to recover the Mobile Network ID
Currently, this information will be available quering DNS A entry:
wakeup.mnc[MNC].mcc[MCC].3gppnetwork.org
For example, if the mobile is inside the network of Movistar Espaņa (214-07), the query will be to A register:
wakeup.mnc007.mcc214.3gppnetwork.org
In the future, a TXT entry should be used, but now, only A records are in use by the Firefox OS reference platform, so the Network ID will have a "IP adress" form.
Anyway, this will be used as an string, so really, the netid will be four numbers between 0 and 255 separated by dots.