iMessage, the iPhone and iPad feature that lets you quickly send messages to each other, has arrived on the Mac desktop in a new beta available for OS X Lion users.

The new beta app, called Messages, which will be eventually "baked in" to OS X Mountain Lion as standard, will replace iChat on the desktop and allow Mac users to chat with their iPhone, iPad, and iPod touting friends without racking up SMS charges as long as they've got an internet connection.

Users will be able to send messages between Apple devices as well as share photos and video up to 100MB - something that could prove dangerous if you are on a tight data leash or roaming.

As with the iOS version the desktop, iMessage will let you send messages to the email address associated with a friend’s Apple ID, or to their phone number, and from what we've already seen it will give you a text message like service from your desktop to your phone without the big text message bills or the need to have a phone number in the first place.

Taking things one step further and trying no to just be a Skype replacement, the new system will also support group messaging:

"You can send a message to several friends by adding multiple recipients to the address field, just like you would with a group email. When friends reply, everyone sees all of the responses."

The idea is the new iMessage service, which will only work within the Apple device ecosystem, will replace simple one line emails and the need to send SMS text messages.

Like BBM you'll get message and read receipts so you know your mates got the message - no excuse for not seeing it - and for the desktop version there will be AIM, Yahoo!, Google Talk, and Jabber support as previously found in iChat.

Like iChat and other new apps in Mountain Lion, iMessage will get its own dedicated app that lists previous conversations, so you can catch up where you left off regardless of the device you've been using, and unlike Skype, the app won't feature a list of buddies to select but instead focus on the conversation threads. As you might expect, you'll be able to FaceTime users at the press of a button, and new notifications will also automatically appear in the new Notification Center when it eventually launches later this year.

The iChat name will be killed when Mountain Lion launches in the summer.

Users can try out Messages by downloading the beta for Lion at www.apple.com/macosx/mountain-lion/messages-beta/. The Messages beta will be available on February 16. The final version of Messages will be available in Mountain Lion.

- For more news on the latest from OS X Mountain Lion check out our dedicated Mac OS X homepage.