Dual Sim mobile phone is a phone that can run the 2 different SIM cards at once. Dual SIM mobile phone very useful for cheaper plan with your mobile operator would like you can call or SMS to make the same operator with the destination number.
I personally have never seen a dual SIM mobile phone before, even a dual SIM unlocked phone and some time if I want to make a call on different cellular operator number, I have to change the SIM card manually by my phone back cover pull out my cell phone battery and replace the SIM card with the same mobile operator SIM card as the destination. All this would never happen with a dual-SIM phone, like you have another option for mobile operators, the SIM card.
Of course, a dual SIM mobile phone has the standard features like good camera, multimedia player and internet access. These functions in a dual-SIM phone would it completed more, but I think it would be the price too expensive to get everything back to the mobile phone manufacturers strategy on how to make a mobile phone with dual SIM option but with full functionality and of course a very reasonable price. This unlocked a few dual-SIM phone that you can verify it, I think the two dual-SIM phone, the features I mentioned above.