"Our goal, when the T-Mobile G1 becomes available in October, is to provide affordable, high-speed data service allowing customers to experience the full data capabilities of the device and our 3G network. At the same time, we have a responsibility to provide the best network experience for all of our customers so we reserve the right to temporarily reduce data throughput for a small fraction of our customers who have excessive or disproportionate usage that interferes with our network performance or our ability to provide quality service to all of our customers. We removed the 1GB soft limit from our policy statement, and we are confident that T-Mobile G1 customers will enjoy the high speed of data access over our 3G network. The specific terms for our new data plans are still being reviewed and once they are final we will be certain to share this broadly with current customers and potential new customers."
Source: Phone Scoop