@timmewinsa:IMO At the moment cross platform phone apps developed using HTML5 are likely to be a compromise in terms of getting the best out of the mobile platform - but the plus side is you only have to have a single HTML5 savvy team or person!  The argument for proprietory is you will get the best out of the platform, in terms of bling and performance, but at the cost of multiple development teams/people.

My advice is to talk to a developer who understands the jist of what it is you are trying to achieve.  If it is not too complex then HTML5 may well be the way to go.