The NIC that i mentioned is probably you are refering as conversion unit. In that unit you do not convert the GSM MAP messages to IS-41 or visa versa, what it does it that it provides the authentication support for the mobiles, and emulates a HLR for that.
i doubt that the mobile that you are talking about is available commercially. Any ways i will be more then happy to see any information on that.
Lastly the RUIM is very much in there as that is the current mechanism to provide plastic roaming between CDMA and GSM.