Think I should mention that on my galaxy y duos, any of the sim can do 3G/data. Only one can do it at a time and you can select sim1/sim2 be the data sim. There is SIM menu that lets you select the sim to use for calls/txt. Again, this can be changed at will. By toda's standards, it's a old phone. From looking at the Moto G reviews, it gives you the option to select the default sim for calls/txt, or it lets you select it as you initiate a call/txt.

The specs - http://www.gsmarena.com/samsung_gala...s6102-4385.php

See mention of the sim1/sim2 toggle menu here - http://www.gsmarena.com/samsung_gala...view-754p3.php

I have heard of 3/4 sim phones. These are Chinese phones though.