Here is little more clarity on OMH.
There are 2 entities which has to be complaint with OMH for to utilize the OMH advantage to the fullest.
1) OMH handset
2) OMH SIM
Normally GSM's n/w settings are completely stored in SIM, so its very easy to switch between operators.
In case of CDMA RUIM, part of the n/w settings are stored in RUIM and other part stored in Handset.
Part which has information about the subscriber and the operator is stored in RUIM but the information about data exchange is stored in handset.
This is the reason why Samsung used to say that their handsets can support R-World, TATA-Zone and V-bytes. Since they pre-program these data settings in their handsets.
If you observe clearly some Samsung handsets although RUIM based will support either R-World or TATA-Zone but not both.
All these handsets will not support MTS-World(if it exists) or BSNL-Zone(if it exists)
In OMH SIM all the settings are moved to SIM similar to GSM.
With OMH, Manufacturer need not worry about pre-configuring these data settings in their handsets. That is the reason why Samsung didn't speak about TATA-Zone or R-World in relation to Mpower 699.
Simply put Mpower 699 can support any CDMA operator's data zone just by inserting respective operator's OMH SIM.
These OMH handsets can work with even Airtel world(if Airtel starts CDMA operations) just by inserting Airtel's OMH SIM.
To cut the long story short, RUIM only ensures the voice and SMS interoperability but OMH ensures interoperability even in data (including MMS).
To ensure downward compatibility, all OMH handsets will work with normal RUIMs although for data usage you've to program the handset with particular operator's data settings.
To ensure downward compatibility, all OMH SIMs will work with normal handsets although for data usage the data settings present in the handset will be taken against the one present in OMH SIM.