The detail of Mobile Suit Gundam Unicorn was announced at Gundam Expo held on August 21st. It's a 50min x six-episode OVA series and will be released in the Spring of 2010 in Japan.

Sunrise called Gundam UC "Cross-over Contents (diversified project?)", which involve Blu-ray/DVD releases, premiere at special events, streamings, and international licensing. Bandai plans a worldwide simultaneous premiere of the anime at conventions.

According to Fukui Harutoshi, the first episode is based on the volume 1 and 2 of the original novel.

Trailer on Youtube

Sources:
Scan of the announcement
Mainichi
IT Media

Story by: GundamUC

Update
Cast
Banagher Links: Uchiyama Kouki
Audrey Burne: Fujimura Ayumi
Takuya Irei: Shimono Hiro
Micott Birch: Tomatsu Haruka
Riddhe Marcenas: Namikawa Daisuke
Mihiro Oiwakken: Toyoguchi Megumi
Marida Cruz: Kaida Yuko
Full Frontal: Ikeda Shuuichi
Angelo Sauper: Kakihara Tetsuya
Zuberoa Jineman: Tezuka Hideaki
Cardias Vist: Sugou Takayuki
Frust(?) Squall: Koyama Rikiya
Siam Vist: Nagai Ichiro

Source: official website

Updated on Oct 23rd/b]
According to Anime!Anime!, Gundam Unicorn movie will be premiered on February 20th, 2010. The official streaming will start on the same day on Playstation Network (PSP, PS3). The DVD and Blu-ray will be released on March 12th, 2010. The Blu-ray includes English dub and subs in English, French, Chinese, Spanish.

Source: Anime!Anime!