you can try as long as its a cdma phone. If you are going prepaid you have to get the smart phone plan. there is a link on their site if you already have a device and it has to be deactivated from straight talk.
It depends really. GSM (SIM Card Accepting phones) Is a different network than Verizon (CDMA, No sim card) so most of the time, it's not interchangeable.
Unless you root your device, which is a different story.