MCC/MNC display in California and Nevada
From HowardForums Wiki
In California and Nevada handsets that are unlocked and not T-Mobile branded may not show the operator identification on handsets as T-Mobile and may show the operator as Cingular. T-Mobile previously entered into a network sharing agreement with Cingular wireless. Cingular broadcast the network identification as MCC/MNC (Mobile Country Code /Mobile Network Code) 310-17(0) with the result that for non T-Mobile branded handsets it may show Cingular as the network and even show that Cingular is the only network(s) available. When Cingular totally vacates the network it's likely that T-Mobile will change the broadcast ID to that of T-Mobile which is 310-26(0). When that happens all handsets whether T-Mobile branded or not will display T-Mobile. The exception to this will be those who roam on the T-Mobile network and in that case they will see the network name that is in the firmware table of their handsets in the case of T-Mobile that might mean that it will show the operator name as VStream or VoiceStream. For Cingular that might mean that they will see the operator name Pacific Bell.
Source(s): T-Mobile solutions