5GB of data, plus the ability to use as mobile hotspot. Share your data connection with Wi-Fi capable devices: MP3 players, tablets and more. Includes unlimited Wi-Fi access at more than 26,000 AT&T Wi-Fi Hot Spots. If 5GB is exceeded during your monthly billing period, an additional 1GB is automatically provided at a rate of $10 per additional 1GB. Internet tethering over Bluetooth or USB requires iOS 4.0 and iPhone 3G, iPhone 3GS, iPhone 4 or iPhone 4S. Personal hotspot over Wi-Fi requires iOS 4.3 and iPhone 4 or iPhone 4S.
AT&T note: A data plan is required for the life of your iPhone service and cannot be removed in the future.