Can i connect the iphone 4 with net 10?

I bought the iphone 4 online used and the seller does not say if the phone is unlocked. I'm planning on connecting it with net 10 and I'm going to buy the net 10 sim card online. When I look on the net 10 website it asks me for which type of phone it is. One of the options is a gsm unlocked phone or a at&t compatible phone. The iphone I bought online was from at& t. So which of the 2 sim cards should I buy? If the phone is locked will the at&t compatible card work? If not how do I unlock the phone?

You should buy the AT&T compatable card. Because the phone is an AT&T phone that is not unlocked.

But if you are still unsure you should contact Net10 and ask them for sure. You can contact them on their Facebook page if you use Facebook. Or you can call them at their 1-800 number.