iPhone and iPod touch: Understanding subscription Wi-Fi networks

Subscription Wi-Fi networks are public Wi-Fi networks requiring a subscription or payment to use. Subscription Wi-Fi networks are often found at coffee shops, Internet cafes, airports, and other public locations that don't offer free Wi-Fi networks. In some countries, they are sponsored and maintained by wireless carriers. (For example, AT&T wireless hotspots in Starbucks locations). When using iPhone OS 3.0 or later, your iPhone or iPod touch can remember the Wi-Fi networks to which you subscribe. It will automatically connect and log in to the Wi-Fi network when you are in range. Note: The features and troubleshooting steps above may not be applicable to devices sold in certain countries including China. Please see iPhone or iPod touch technical specifications and this article for more information.

Source: Apple - Support - Most Recent - iPhone