Here's a how-to in putting in a SIM to a Samsung Galaxy S4 Mini...
Both the Samsung Galaxy S5 and Galaxy S3 have micro-SIM cards. So, it should work.
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There is a dual SIM variant for the Galaxy S5. However, it's only available for the China market.
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Galaxy S 4G phone - Earbuds -Manuel - new SIM Card
You can purchase sim network pin for Samsung Galaxy S3 from any vendors online like Unlock-Zone.com
you have to put a sim card in every phone, if u e=want to save stuff
u put it uder the sim card ....
When you buy it, it doesn't come with a sim card, but there's a place to insert one on the side. :)
When you switch from iPhone 4S to Samsung Galaxy S5, would you transfer all data from your old iphone to Samsung? It's surely you need to do that. See related link for a video for that, it's easy to use.