there are 2 types of data cards -
1. CDMA based
like Tata Photon+, Reliance CDMA, MTS Mblaze etc.
2. GSM based
like AirTel 3G, Vodafone 3G, Reliance 3G, Aircel 3G, Idea 3G etc.
CDMA based data cards do not require any SIM but GSM data cards need a SIM.
even if unlocked, CDMA based data cards can not be used on another network (like photon+ can not be used on Reliance)
GSM datacards are also usually locked to particular network but can be unlocked and any other provider's sim can be used in it.
or you can look at open market Huawei data cards available at Huawei :: Products - Mobile Broadband - Data Cards Features Comparison Sheet
then you can get any sim and test it in the data card.
Yes I was also using it till it stopped it's service here
Please suggest me which datacard to buy.