Monster Hunter Frontier is an MMO first launched in 2007 on PC, and in 2010 on Xbox 360. Frontier G is an update to that version and is similarly subscription-based, even on Vita. The Vita version will not include every level of the full console game, but it will have "several PS3 worlds," Siliconera reports.
Capcom previously denied rumors that Monster Hunter 4 was on its way to Vita. Check out screens of Monster Hunter Frontier G on Vita on its official site.