Facebook today announced that they're allowing devs to add Like buttons to their apps. Users will have to provide permission for apps to use built-in Like buttons, unlike their web counterparts. Likes through mobile apps will pop up on your timeline, in news feeds and as notifications to friends when appropriate, just as you'd expect. Facebook trotted out Instagram and Foursquare as some of their first partners to implement the capabilities, and I'm sure we'll see plenty more in the next couple of weeks.
There is a slight caveat, however: Facebook says that they won't be approving custom like actions, whereby they can put just about any content they want into the box that's shared online. Now it'll all have to be within a specific format, and developers will have to make the change within the next 90 days.
Facebook's Open Graph is a pretty huge deal, and the implementation of these new Like buttons could significantly improve discoverability of iPhone and iPad apps. If you're a developer and want to know how to build in these new Like buttons into your app, you can check out the Facebook documentation over here.
Are there any particular apps you'd like to see have a Like button? More than once I've wanted to be able to "Like" someone's Twitter status, but something tells me that's not going to happen any time soon.