There are several IMEI number check sites. Have you done a Google search to find any of these sites?
Do you have the device in hand? Is it activated on any network?
When you say locked or unlocked, are you trying to figure out if it will work on a certain carrier or if it is stolen or deactivated for some other reason?
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If the device is active with any carrier *611 customer service should be able to answer these questions for you as well.