iPhone OS 4
The iPhone OS 4 has been released for some time, but it is worthy to be posted. Again.
1. Multitasking.
This has been a long anticipated item for the iPhone OS. It has been finally released into the world. It will only work on the iPhone 3Gs and the iPod touch (3G, 32 & 64 GB models). It will not work on other devices because of lack of adequate hardware.
2. Folders.
Folders have also been anticipated, but to make it work (in 3.0 and under), it must be jailbroken. This will not be needed for the OS 4. If you are worried that you do not have a proper device, there is not limit.
3. Even Better Mail.
Mail has been updated to have even better connectivity and have unified mailboxes.
4. iBooks.
iBooks has been optimized to the 320x480 resolution of iPhones and iPod touches. It has the iBookstore and all features from the app from the popular iPad app.
5. Developer.
The 4.0 SDK gives developers over 1500 new APIs for their apps for the iPhone OS 4.0.
6. iAd.
Say goodbye to Google ads. Say hello to iAd. The new generation of mobile advertisement.
7. Enterprise.
Enhancements for in-house applications for security and compatibly and more.
Well, there you have it. The new iPhone OS 4. Enjoy!
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Compatibly requirements:
iPhone OS 4 Compatibility
iPhone OS 4 will work with iPhone 3G, iPhone 3GS, and the second- and third-generation iPod touch this summer, and with iPad in the fall. Not all features are compatible with all devices. For example, multitasking is available only with iPhone 3GS and the third-generation iPod touch (32GB and 64GB models from late 2009).
iPhone 3G 
iPhone 3gs
iPod touch 2 & 3 Gen. 
iPad (in the fall)
The iPhone OS 4 will NOT work on the first generation iPhone and iPod touches.
