Microsoft has finally decided to take mobile computing seriously. Well it's about frickin' time.Yesterday at the opening of Mobile World Congress in Barcelona, Microsoft CEO Steve Ballmer announced Windows Phone 7 Series. The new mobile OS is a desperately needed new direction for Microsoft's belated challenge to the iPhone, Android phones, the Blackberry, and others.First impressions of the phone have been positive and, in some cases, glowing. Gizmodo calls it the "most groundbreaking phone since the iPhone." The vibrant, big-lettered Zune HD interface is getting the most praise. The touchscreen UI improves on Windows Mobile 6.5 (and looks nothing like it) with simple, customizable tiles on the Start screen that provide quick access to your favorite content. The phone is efficiently organized around hubs labeled People, Pictures, Games, Music + Video, Marketplace and Office. And these hubs are dynamic. For example, the People hub is not just a list of contacts, but a real-time stream of updates about your friends pulled in from Facebook and Windows Live (if you have any friends who actually use Windows Live). There is no support for Twitter yet, but that will change I'm sure. If you've pinned a friend to your Start screen, his or her latest status and photo will update in real time. The Music + Video hub basically replicates Zune HD's software within the phone.Click here for an extensive overview of Windows Phone 7 Series.I'm admitedly excited that Microsoft has a sexy, intuitive UI and is finally going to give Apple, Google and RIM a run for their money in the mobile space. There is a lot we still don't know \u2014 price, battery life, hardware design specs \u2014 but Microsoft now has a mobile challenger, by God.But it also has serious challenges if it wants to keep up with, let alone surpass, iPhones, BlackBerrys and other established mobile players.I would say the first big challenge is the name: "Windows Phone 7 Series" is way too long and clunky. You feel like you might trip over something when you say it.It's as if the Microsoft branding folks took the words "Windows" "Phone" "Seven" and "Series", threw them up in the air and this is how they landed. If they landed a different way the name would be "7 Series Phone Windows."A shortened nickname is inevitable. Why is the word Series even there? How about WP7? "Hey buddy, can I borrow your WP7 to make a call?"Dreadful branding aside, here are three more serious challenges for the Windows Phone 7 Series.Launch Too Far AwayWP7 will not launch until the 2010 holiday season. Yikes. Why not just wait until 2012? I'm all for building hype but Microsoft is giving Apple, Google, RIM and Nokia way to much time to release new phones and updates. And they will. Google is slated to roll out a multi-touch version of Android this week. iPads are due in March and April and a new iPhone is due in June. The list goes on. Seven months from now WP7s may not be so sexy.The AT&T FactorMicrosoft CEO Ballmer confirmed that WP7s will appear on all four major U.S. carriers, but AT&T will run the first ones. Yes, that AT&T, the one with customers so angry at spotty network service that they tried to overwhelm and shut down the network last December. AT&T, being the sole iPhone wireless carrier, cannot handle the amount of data that multimedia-drunk iPhone users are consuming. Hence, its network is squeezed and a nasty backlash has followed. Given AT&T's current bad reputation, and also the amount of iPhone users it supports, it seems like a poor choice for the first WP7s.Little Control over Hardware DesignWP7's will be in the same boat as Android-based phones: The hardware is designed by someone else. Whether the phone maker is LG, Samsung, HTC or Sony Ericsson, Microsoft won't have much of a say in how the hardware looks. (HTC has confirmed it will launch the first smartphone running WP7 in the fourth quarter of this year).Apple, RIM and Palm have the advantage of developing both the hardware and software. Google does not make hardware, but it rectified this problem somewhat with its branded Nexus One phones. But Microsoft will have to rely on hardware makers to make the body as sexy as WP7's soul. And to compete with the iPhone for consumer attention, you better have a hot body.Shane O'Neill is a senior writer at CIO.com. Follow him on Twitter at twitter.com\/smoneill. Follow everything from CIO.com on Twitter at twitter.com\/CIOonline.