I am looking for such a thing as well.  I just found http://www.3dar.us/ which seems like a good place to start for iOS.  It isn't open source, which is a bummer.
Edit:
I have tried out Mixare, and I am really impressed by it.  I have compiled it for Android.  The only part that gave me a hard time was making sure the project was using the Google API v10, and that I had it installed.
Mixare does easily support Points of interest (POI)  Check out their wikipage for more about it, basically you just feed it JSON.  I am personally going use CouchDB with GeoCouch to serve up data, with free hosting provided by iriscouch 
The JSON should look like the following:
{
    "status": "OK",
    "num_results": 1,
    "results": [
        {
            "id": "2827",
            "lat": "46.43893",
            "lng": "11.21706",
            "elevation": "1737",
            "title": "Penegal",
            "distance": "9.756",
            "has_detail_page": "1",
            "webpage": "http%3A%2F%2Fwww.suedtirolerland.it%2Fapi%2Fmap%2FgetMarkerTplM%2F%3Fmarker_id%3D2827%26project_id%3D15%26lang_id%3D9"
        }
    ]
}
The most wonderful thing is that it is GPLed!