When a customer runs out of data on an AT&T Go Phone plan, several options become available. The customer's data service will typically be slowed down, reducing browsing speeds until the next billing cycle starts. However, basic texting and calling functions will remain unaffected. Customers can also opt to purchase additional data through the AT&T Go Phone account management system or AT&T applications. These add-on data packages can provide a temporary solution until the customer's next renewal date. Additionally, it is a good practice for customers to monitor their data usage regularly to avoid running out unexpectedly. For detailed information about any specific plan, available options for purchasing additional data, and upgrade possibilities, it is advisable to check the most current information on the official AT&T Prepaid website.