Longer answer is: there are two ways to approach mobile. The first step is developing a website using best practices. Things like making sure your menu/links are not too small that a person on a phone would be unable to click it with their thumb. On every website we work on, we start with a mobile mindset that ensures your site will work on mobile devices.
We also will advise you through out the web design process as to what works best on mobile phones. Some things like flash and some images don't work well on mobile phones, but we have ways that actually work better so that you can still have what you need and have your site work optimally on a mobile device.
The second step is optional and involves some extra work. If you expect a large number of mobile users, it makes sense to set up your site in a way that allows them to have a customized experience. You can use the same pages and content, but we'll build a layer on top of your site that formats to work naturally the way smart phones are designed. We've developed everything from native apps to web apps to mobile sites, so we're happy to talk with you about what it would look like for your site to be mobile.