Apple’s 1OS 4 is now available for iPhone 3 and iPhone 3GS users.

This comes three days ahead of the Thursday release of the iPhone 4G, which will feature the new OS.

Here’s a breakdown of some of the new iOS 4 features and some tips for installing on a 3G.

Multitasking

You’ve always been able to multitask with iPhone features like the music player, but the option is now available for third-party apps.

However, instead of having all device resources available to every running app, iOS 4 lets only seven app services run in the background.

Apple’s new multitasking is essentially a “program hold”, which is not the same as what you can do on a Mac or PC, where the app keeps running in memory.

Home screen folders

The new iOS 4 allows you to create home screen folders.

Use a long press on the home screen so the icons “jiggle.” You can the take an app and drop it on top of another to create a folder. You can put up to 12 apps in one folder.

It’s pretty simple to use but not radically different from what is offered on Android.

E-mail streamlining

The iOS 4 has unified in-box that contains messages from multiple accounts. You can’t access individual folders from the universal in-box, but you can delete and move messages.

You’ll also be able to organize e-mails by thread, move directly to individual in-boxes, and open attachments with a chosen app.

Geolocation

Geolocations lets you see where you took your pictures on a map and sort your images by location. Brilliant for travellers.

Camera improvements

The camera app runs faster. You’ll have to wait for the iPhone 4 to get a 5-megapixel shooter, but iOS 4 adds a 5x zoom for the still camera.

Search text messages

You can now search your text messages in the same way that you could previously search emails. Pretty useful!

Spell check

Rather than the old autocorrect system, the iOS 4 has a spell check feature that underlines unrecognized or misspelled words in red and offers you a list of suggested corrections.

Does iOS 4 work with a 3G handset?

Make sure you have already installed iTunes 9.2 prior to updating.

Connect your device to your Mac or PC using dock connector cable while iTunes is still on. When iTunes identifies your device click on ‘Check for Updates’ button.

Here’s the link: apple.com/iphone/softwareupdate

Apple says that the whole process could take an hour and is slow at the moment due to high demand.

Now read this: iPhone 4G features and reviews

Tags: iPhone, Apple iOS 4, technology, iPhone apps, new iPhone, iPhone 3G, iPhone 4G, multitasking iPhone