To scan a barcode, you'll need to download the Barcode Scanner app.
The Barcode Scanner app will allow you to scan barcodes for quick downloading of Android apps.
Enter your e-mail address below, and T-Mobile will send you a download link for this app. Open the e-mail from your T-Mobile G1 and follow the link to the download page. Or head to the Android Market and search for it under ZXing.