About 72 hours from now at the annual WWDC conference Apple chief Steve Jobs will explain why you should entrust your digital life to his web servers. Here’s the best information we have so far on what shape Apple’s new cloud service will take:

It will be called “iCloud”. This is perhaps the only thing we know for sure, thanks to Apple’s surprise move of outing its own product early in a brief press release:

“Apple will unveil…iCloud®, Apple’s upcoming cloud services offering.”

This week the company also took control of the web domain icloud.com, paying a reported $4.5m.

It will already have your iTunes library ready to stream to any device. We know almost-for-sure that an online music locker that stores your music for easy access will be a major part of iCloud. Competing offerings from Google and Amazon require you to laboriously upload tracks you already own. BusinessWeek says that won’t be so with Apple’s service:

“Armed with licenses from the music labels and publishers, Apple will be able to scan customers’ digital music libraries in iTunes and quickly mirror their collections on its own servers, say three people briefed on the talks.”

Yesterday it was reported that Apple has signed a deal with record label Universal that - combined with deals with with EMI, Warner, Sony and Universal - brings all four major labels on board. In contrast, neither Amazon nor Google got or has record label approval for their cloud music plans.

It will be hosted in a 500,000 square foot data center in rural Carolina. The huge facility is visible in Google Earth.

No one knows what is inside, but the scale of the datacenter makes it one of the biggest around (Facebook’s recently opened data center covers only 147,000 square feet). One analyst told US Today:

“This may be the most powerful data center ever, outside of government”.

It will start out mostly free, then become a subscription service. The new iCloud service will replace MobileMe, an online email/calendar/contacts and file storage service that currently costs $99 and that Steve Jobs thinks let his company down.

The LA Times reported yesterday that:

“[T]he service initially will be offered for a free period to people who buy music from Apple’s iTunes digital download store…The company plans to eventually charge a subscription fee, about $25 a year, for the service. Apple would also sell advertising around its iCloud service.”

An earlier report from CNet also claimed iCloud’s music streaming would launch as free-for-now. Google’s free cloud music locker will also start to cost at some point in the future, the company has said.

It won’t make the iPod obsolete…yet. Many commentators have said that Apple is about to make relying on cloud storage mainstream, but the company is very unlikely to take the hard drives out of its products. Speaking to CNBC, Gartner analyst Ben Pring pointed out that for many people clouds will remain just a part of the weather forecast:

“People will be running physical hardware and saving things to hard drives until long after we are gone…These services are aimed at that younger demographic, whereas for the Heartland and middle aged Americans, there are lot of security concerns and emotional comfort concerns about not being able to hold something in their hands.”

The continuing revelations about how hackers were able to extract personal details and credit cards from Sony’s cloud servers will - justifiably - heighten those fears.