LG Electronics announced an agreement to provide YouTube on its mobile phones.

"People want to be able to capture interesting moments with their cell phones wherever they are and whenever they want," said Steve Chen, Co-Founder and Chief Technology Officer for YouTube. "We’re excited to be partnering with LG to give people the opportunity to enjoy YouTube for watching and sharing those moments."
LG first announced its agreement to pre-install Google's services on its handsets in March 2007.
As a first step in this partnership, LG recently launched the LG-KS10, which features Google search, Gmail, and Google Maps for mobile. The LG-KS10 first hit shelves in Italy this past April. See also the new Google Phone LG Chocolate LG-KU580.

The LG YouTube-enabled mobile phones will be available worldwide starting at end of this year.
Via this LG press-release (Korean).

The Apple iPhone supports Youtube today.