Is using 1 sim card between multiple phones allowed?

    I am a bit of a techy, and I love to play around with all forms of technology.  Because of this, I don't want to have to limit myself to just one type of phone.  I currently have a Nexus 5 and love it.  I would however like to try out a Windows phone too as I have heard good things about them.  If I bought another unlocked phone, could I swap the sim card between them as I please depending on which phone I want to use that day or is this not allowed?

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