Could I buy a phone from another company switch the sim cards and still use it?

I would like to know because I saw a cell phone that I might buy and it is not in my network but I know that you could switch sim cards when you buy an unlocked cell phone so I wanted to know is it for every phone basically... If someone could explain why or why not that would be helpful. Thank You.

Could I buy a phone from another company switch the sim cards and still use it?
no it wont work because the sim card is programed to work for that company and not the other.
Reply:Check out this article about unlocking phones.
Reply:No, you would have to unlock it because every company has their phones so it only works on their network. But phones from Sprint, T-Mobile and AT%26amp;T all use sim cards so you could just unlock it.
Reply:Not every phone - only GSM phones. CDMA phones (Verizon, Sprint, Alltel, MetroPCS, Cricket, US Cellular, etc.) don't use SIM cards.