What are dual Sim cards?

What are the advantages of cellphones with dual SIM cards?

• I have seen a few models, they say it has GSM + GSM and dual standby. I have two cellphones, one for business, work etc and the other personal. So when I am like not in a mood to talk or anything and the phone rings, I figure out if it's the work related phone or the personal one and accordingly whether to answer it. So I don't understand the logic of a dual SIM phone. Can someone please explain? Also what is dual standby? Thanks.

• Answer:

  It is a mobile phone that allows you to insert two SIM cards at the same time. So, with this mobile, you can insert 2 different SIM cards that allow you to make and receive a call for both numbers by using one mobile phone. 2 numbers standby at same time. You can choose one of them to dial out or receive the call at anytime. ( Separate SMS/ phone books/ call history folders- both number can receive or send SMS) .Therefore: you don't need to purcahse another mobile phone if you have 2 numbers.