According to a study of mobile phone usage, mobile phones account for over 15% of North America's Internet traffic as of July 2013. That's up from 9.4% just a year earlier. As these numbers continue to increase, so too does the importance of a businesses website being able to be accessed via a mobile phone.
You'll notice that these figures don't even include iPads and other tablet-sized devices.
Modern web design techniques, such as responsive design, enable websites to automatically adjust themselves to accomodate the large number of different devices with varying screen sizes and capabilities.
For many people, their mobile phone is their primary, and sometimes only, means of accessing the World Wide Web. To help maximize income, it is critically important for business owners to make sure that their website is available to as many people as possible on as many devices as possible.
If you'd like help creating or improving your businesses website, please let me know.