Depends upon what the device market breakdown among your potential customers.. Symbian-everything before ^3 devices not fully html5 WM-everything before WM7 no

Depends upon what the device market breakdown among your potential customers.. Symbian-everything before ^3 devices not fully html5 WM-everything before WM7 not fully html5 BB-everything past 4.4 is almost full html5 Android- 2.1 and beyond is full html5 iPhone iOS 4 is full html5 I would start examining frameworks such as PhoneGap, QuickConnect, etc to see which covers the best as far as html5. Of course this depends upon whether you need to access native device features as at the moment the un-spec HTML5 through webkit only has camera, audio, geolocation, sms.