AT&T's entry-level smartphone data plan that offers 300MB for $20 a month will no longer be available to new customers beginning August 21. Additionally, the current 2GB plan that costs $30 will be replaced by a $30 plan offering only 1GB. A new $40 plan will offer 3GB, while $60 will provide 6GB, replacing today's $50 5GB plan.

On the plus side for customers who buy the lowest-cost data plans, AT&T is changing its phone access charge to $20 a month per device. You need to add the data and device access charges together to get the monthly cost before miscellaneous fees. Currently, AT&T imposes a $25-per-month access charge on plans with 5GB or less and $15 on bigger plans. Going forward, the $20 charge will apply regardless of size, with some exceptions—two-year contracts will still have access charges of $40 a month.

These changes are part of a revamp of AT&T's Mobile Share Value plans. In some cases, the new data prices offer better value. For example, it will cost $90 to get 16GB, while today it costs $100 for 15GB. The dollar-per-gigabyte value gets better from there. While today you'd pay $175 for 25GB and $225 for 30GB, next week it will cost $110 for 25GB and $135 for 30GB. The plans come with mobile hotspot capability, rollover data, and unlimited talk and text.

You can find the current prices here and the new prices in yesterday's AT&T announcement. Existing customers will be able to keep their current prices and data allotments.

The new plans eliminate automatic overage charges. Instead of being charged extra when you exceed the data cap, speeds will be reduced to 128kbps for the rest of the month. Customers who want higher speeds for the rest of the month would have to switch to a more expensive plan that offers more high-speed data. The change in price is prorated by the day, and customers can switch back to a lower-cost plan the next month, AT&T told Ars. Customers can make the plan changes in a mobile app, online, via phone, or in an AT&T store.