You can use our HTML5 map control royalty free (we only license our web services). Our freehand drawing support (which I don't believe Leaflet offers) works nicely in the iOS and Android browsers. http://apps.mapdotnet.com/HTML5/iSDK/isc.rim.isdk.spatialQuery.htm
With your drawn shape you can pass it to through the REST services to perform a spatial query on a table in PostGIS or save that draw shape into PostGIS. The other big advantage is our map rendering service which can render map tile overlays on-the-fly from PostGIS table. This allows you to render lots of data on tiles server-side so you can overcome limitations of rendering large amounts of data client side.
In case you're interested, we're working on advanced geospatial data collection tool based on Kendo UI mobile that will showcase how to do the advanced drawing and shape editing mentioned above.