My Thai SIM card goes in my smart phone and my home SIM card has often been installed in a small light Nokia phone, just in case anyone needs to contact me.

However, since most of the people who would contact me in an emergency have Skype, What's App, We Chat & e-mail, there is no longer any real need to put my home SIM in a second phone. Also no risk of incoming calls when I'm enjoying the nightlife.