I am thinking about buying an HTC Thunderbolt to replace my Droid X. My question is, do I need to also buy a 4G SIM card? If I buy the phone off say eBay and it does not have a 4G SIM card do I just need to buy one from Verizon?
You will need to obtain a 4G Sim Card in order to activate the HTC Thunderbolt your intend on purchasing. You can order a 4G Sim Card via logging into My Verizon and even activate the Thunderbolt online. Before purchasing your device, first check that the ESN (Electronic Serial Number) is cleared so it can be activated on your line. Please bear in mind that if the device was lost or stolen, it cannot be activated. This is because the ESN may have reported to us in this status thus preventing the activation even if you get a 4G Sim Card. Here is a link for for checking on the ESN number online. You can use the Backup assistant to back up your contacts on your current phone before activating the Thunderbolt to have them available for transferring. I hope this helps.