How to find out what model my iphone 3 is?

Bought on eBay over 3 months ago. How do I tell which model it is? 3g or 3gs?

Go to Settings>General>About and see your model number MBXXXLL/A. Next, look the model number up online to find out.

You can run its serial number (not the whole number) on the everymac website. It's not just macs.

http://www.everymac.com/ultimate-mac-lookup/

There's no 3 to begin with. As far as figuring out which, if it can only update to 4.2.1 then its a 3G, if not, 3GS.