Thank you YouTube, for your rapid & effective launch of your mobile version! Following what seemed like a typical operator-approach exclusivity model with Verizon, looks like you really mean mass-market.
Good news - No client needed, just come and get it with any internet 3G phone! That's exactly what this industry needed for a long time - an Internet giant meaning business & leveraging the Web's open model on the mobile industry. Most other internet content players view the operators as the "plug number" in their broken revenue model, trying to sell OPC (Other People's Content) in traditional content models, overlooking the end-consumer reluctance to pay premium for content mobility.
Way to go, with respect to the general business strategy of going it alone! However, in the even more important part of the strategy - product-wise - YouTube still has a lot to learn about the mobile space, its past failures and mainly - the mobile life of users. The standard portal experience on mobile has made it hard, even for the most advanced users, to become addicted. Generalized & thin content lineups make it impossible for service providers to cater to all segments & individual tastes, which is needed to make a product truly mobile.
The products that DID succeed on mobile were those that enabled deep personalization & uniqueness to its users (Phone decoration, ringtones etc.).
Heavy browsing requirements for little content is something every mobile user has on his operator portal. At least there the content is local which means it is somehow targeted to its audience. With YouTube , its the same popular stuff consumed by all, with no value-add for mobility.
When I am on my mobile, I normally have a minute. Maybe two. The only way I will choose to go on the internet is if I know I am 2-3 clicks away from something that will Hook me up, and will be unique & forward-worthy. For that to happen, content sources will have to be much more varied than a YouTube. A community system will have to be working for me - Scouring the web, fetching content, filtering it for mobile consumption, connecting me with peers' content, and more.
In some sense, YouTube will always remain YouTube - an eclectic mix of user-generated & commercial content, targeting mainly the young and the bored. To truly mobilize the internet video revolution, a new type of access mode is required - one who puts the user in the center!