Marvel Vs. Capcom 2 is coming to iPhone and iPod Touch on Wednesday, April 25, Capcom has announced via their Capcom-Unity blog.
While the iOS version boasts all 56 fighters as it's console and arcade couterparts, the screenshots provided by Capcom don't show the on-screen touch inputs you'd expect from an iOS fighter. There's no clarification, but if the PlayStation Vita version of Ultimate Marvel Vs. Capcom 3 is any indication, you'll probably just tap the screen repeatedly to fight and watch your team go.
There's also no mention of price, but $5-10 seems like a safe bet.