how do I know if the cell phone that I have (new) is unlock or lock??

it is a Samsung SGH-i550

my husband bougth the cell on e-bay and they send it from usa...

it is brand new, and as far as I know my husban was using the phone but sudenly is not showing the Network

what it's wrong??

See More: Little problem with mi SGH-i550 (Network not working)