Can you use a phone with any company that uses sim cards?

Can you use a phone with any company that uses sim cards? Like say I had an old phone from t-mobile and I was added to another company that uses sim cards....could I just switch the sim cards or would I have to get a completely new phone?

Can you use a phone with any company that uses sim cards?
You must make sure the other company uses the same type of network. Some companies that offer the PTT feature use iDEN networks, while most companies such as T-Mobile use GSM networks. You cannot use an iDEN phone on a GSM network, or vice versa. Hope this helps.