I thought hotels were required to report to immigration when a foreigner checked in/checked out. How would they be able to do this without a passport number? If the pink ID card does not contain your passport number, then the hotel must be registering you as a non-foreigner, possibly in order to circumvent the TM-30 reporting requirement. That is an incentive for hotels to accept the pink card in lieu of a passport, but I wonder if that practice is kosher from immigration's standpoint, and if some hotels in some areas have been fined for doing this, which might explain why there is inconsistency about whether pink ID's can be used universally to check in to hotels.
