cross platform mobile html5 site

hey, I`ve been asked to develop a cross platform html5 mobile site proof of concept for a client. i`m in need of some consulting as to how build one code properly that would run well on iphone, android,very advanced symbian, future windows phone and perhaps advance blackberry. some of the issues i need addressed are: the limitations i need to consider when i want to build a cross platform mobile site what types of mobile device/browsers will be able to run my site use of html5 my most immediate need is for an hour or two of consulting. some by phone(i`ll be calling) and perhaps some by mail. if all goes well i`ll probably need more time for consulting and help with building sites(will be paid and determined in the future according to events).