Finding the firmware/software version, serial number, or space available on the iPhone 3G can sometimes elude even the most experienced user. Here’s how to find this information though.

1. From the Main Menu, select Settings.

2. Select General.

3. Select About.

You will have a screen that includes all of the following information:

• Name of your phone network
• Number of songs, videos, and photos
• Total storage capacity
• Space available
• Software version
• Serial and model numbers
• Wi-Fi and Bluetooth addresses
• IMEI (International Mobile Equipment Identity) and ICCID (Integrated Circuit Card
  Identifer, or Smart Card) numbers
• Modem frmware version of the cellular transmitter
• Legal information

Source: iPhone Users Guide