Apple has revealed two upgrades to the iPhone, enhancing battery life and upgrading the touch-screen surface of the much-anticipated mobile device. 

The news comes just 11 days before the device is slated to go on sale in the US on 29 June.

When Apple unveiled the iPhone, the company said that the device would offer five hours talk time and 16 hours audio playback.

The upgrade means that users can expect eight hours talk time and 24 hours audio playback from a single battery charge.

Apple has also replaced the original plastic screen with a more durable optical-grade glass which should be much less prone to scratching. Users have reported problems with the screens on some iPod models.

The company released data on the expected surfing and video times of the new device, promising six hours internet use and seven hours video playback on a single charge. Previous estimates were for up to five hours for each operation.

The iPhone will be able to operate for 250 hours in standby mode before requiring a recharge. The company had previously given no estimate for standby time.

Apple isn't disclosing how it achieved the increase in battery life. An Apple spokesperson would only tell vnunet.com that the move was "part of the development process". 

The iPhone is still on target to go on sale in the US on 29 June. The 4GB model will cost $499 while the 8GB model will be priced at $599. The iPhone is due to launch in Europe in the fourth quarter of this year.