Hypothetical situation: I will have the HTC One M8 with a T-Mobile SIM, on a T-Mobile plan, this Thursday(today being Wednesday). The HTC One M8 is the phone I chose over the Nexus 5, Galaxy S5, iPhone 5s, etc, but I can see myself wanting a different phone or wanting to upgrade, in the future. So, say the Nexus 8 phone comes out two years from now, and I want it, ALONG WITH the HTC One M8 I already own. Could I buy the 'Nexus 8', not put a dedicated SIM card in it, but switch between my 'Nexus 8' and HTC One M8, by simply taking the SIM out of one and putting it into the other? I know that phone reviewers do this since it allows them to get a user experience for all phones they get sent or buy without having to pay hundreds on a plan for each one. That is why I would do it, so I could basically have two potential smartphones without having to pay for the usage of the one I'm not using ATM. Also, would it make a difference as if the 'Nexus 8' is unlocked, or a T-Mobile brand? And could I buy it from T-Mobile and just not put that SIM card in? Basically, I need to know what my options are here. Thanks guys, you are such an awesome community.