I lost my iphone! If someone found it can they use it?

Can they erase everything and use it as if it was one they bought? I can't believe i lost it and i didn't even have a lock on it! Ugh.

You should be able to deactivate the phone if there's no tracker on it, and if its an iPhone and you have the app find my iPhone you can turn the service off. Otherwise deactivate it and replace it until/if you find it so nobody can use your phone.

Use iLocalis. This lets you log in to the website to find your missing iPhone. You can also log in and send yourself a message. If the sim card has been changed, you'll also be able to get the thief's new phone number.

I believe they can.