Is there a way to reset Samsung Gravity 2 Phone Lock?

I bought a phone from Ebay, It is a Samsung Gravity 2 and there is a startup phone lock on it. The guy swares up and down that he did not lock the phone but something has to have happened since he said that he tested it. So is there any software or master code that I can put in? I have tried the ones that people say to put in like *2767*2878# but I think that is if you can put them in like you would a phone number. It wont let me do it, just comes up with "Phone Lock" and a box to enter 4 - 8 digits and I cant get it. What can I do?