The Palm Pre has officially gone on sale in Sprint, Best Buy, Radio Shack and Wal-Mart stores across the United States.

Tipped to become the most successful touchscreen iPhone-challenger yet, the Pre has enjoyed a warm response from critics and consumers alike.

As such, it's widely expected to become the first phone to at least come close to living up to an 'iPhone-killer' billing.

The Pre has a 3 megapixel camera, a 3.1-inch multi-touch screen, 8GB of storage, full connectivity including 3G and Wi-Fi as well as a removable, rechargeable battery.

What's more, Palm has enabled electromagnetic induction charging in the Pre – a method of charging the battery without the need to plug the device into anything.

Anyone who buys the Pre can use this functionality by purchasing Palm's Touchstone wireless charger, which went on sale ahead of the Pre handset launch last week.

Ground breaking interface

Another of the most innovative features is the 'Cards' system. Using the centre button at the foot of the device, users can see a full set of all the open windows, and either flick through them or 'throw' them up the screen to discard.

palm pre

KEYPAD: unlike the iPhone, the Palm Pre has a slide-out QWERTY keyboard

The Palm Pre also features a gesture zone where users can swipe around to navigate through applications, or drag up the menu loader to access a full range of applications.

iPhone-like interaction

It's also similar to the Apple iPhone in that it features a sexy multi-touch screen, meaning the familiar 'pinch to zoom' functionality present in the iPhone has finally made its way to another portable device.

It's the kind of slick, innovative interface we haven't seen since the iPhone came out – and that's what has caused the biggest stir.

A UK launch date for the Palm Pre has not yet been confirmed, but word is that it'll be an O2 exclusive, and will be available before the end of the year.

We will soon publish our in-depth review of the Pre, but if you can't wait to read more, check out these Palm Pre stories already live on TechRadar:

Palm Pre: reviews from around the web

10 touchscreen rivals to the Palm Pre

How the Pre could revive Palm's fortunes

Palm unveils the Pre - a genuine iPhone killer

O2 to launch Palm Pre in the UK before Christmas?

Hands on: Palm Pre preview

Palm Pre can sync with iTunes like an iPod

Palm Pre vs Apple iPhone: the verdict

And more Palm Pre stories...