Clare,

The purpose of a .mobi site is to allow visitors to view a website on their mobile device. It is really not a question of either/or. A .mobi site is specially designed and coded to function well on mobile devices. If you think your client's site visitors would benefit from searching his website on their mobile device, whether to make a purchase or requests for information, then it may prove beneficial to him. I would not substitute it for a website that can be viewed well on a laptop or desktop. I would have a .mobi version of your client's .htm or dynamic website developed as well. You can let his site visitors know it exists by announcing it on his homepage or in his News section and you can put a link on his .htm website that re-directs to his .mobi site. If it is search engine optimized, the search engines will scan and index the .mobi web pages and make them available in the search engine response pages.