There are two mobile plugins that will make elgg mobile compatible. Also I read there's a native app for cellphones, however I'm afraid it is commercial.

Rodolfo Hernandez

Arvixe/Elgg Community Liaison

mobile apps? depends which area u r looking for ? mobile, bybrid or native; in increasing order of development difficulty level ;) but the first two are not that heavy to aim for if you're interested in and looking for some real fun development and new coding..