If the serial number begins with 5K then it's a refurbished. So yes you do have a refurbished iPhone. All refurbished iPhones include a new battery and outer shell as well as the replaced parts. Besides the different SN there is no way to find out if it's a refurbished iPhone or new iPhone.
i just got a refurb first gen. iphone as a replacement. i think they used the screens from the new iphones when they refurbish the old model because the screen has a bit of a yellow tint like the new ones.
If the serial number begins with 5K then it's a refurbished. So yes you do have a refurbished iPhone. All refurbished iPhones include a new battery and outer shell as well as the replaced parts. Besides the different SN there is no way to find out if it's a refurbished iPhone or new iPhone.
While not an exact science, you can often tell based on the activation date, which is reflected by the warranty end date.
For example if you look up the Thread Starter's serial number you will see the APP expires on July 17, 2010 while the phone support is indicating that it ends on April 7, 2011. A clear sign the refurb was activated today.