I don't think there is a phone which allows you to insert 2 sim cards. But there is a device called Dual Sim Card Holder that can do this.
Dual sim card holder allows you to put 2 sim cards into 1 mobile phone. You can switch between 2 lines to download sms and to call in/out. Unlike physically change sim card, your phone call history and sms will not be lost.
It also have a both on line function which allow the lines to be switched over in certain minutes of time. (You can also disable this function)