If you already have a website now a days it is best to have a mobile app as well. More and more people use web through mobile and hand held devices and reaching out to these people will boost visitors to your website.
There are many frameworks for mobile app development. Some are best suited for complex native apps and some are best for simple static informative type of apps. One of the frameworks that allow you turn your website into a mobile app is PhoneGap. You can do much more with it but since it uses WebView or UIWebView which is essentially a browser in a mobile device, you can easily display your website through a PhoneGap built application. PhoneGap is also totally free. It is better to make your website mobile friendly such as easy to use and navigate in small phones and tablets.