We've found that there's a lot of confusion about the difference between mobile apps and mobile websites, even amongst many so-called developers - believe it or not! The difference is very simple. A mobile app runs natively on your mobile device and must be installed on the device; many can be used regardless of whether you have an internet connection. A mobile website is a version of your website that is stripped down to make it faster to load on a mobile device and easier to read and navigate on the small screen. Usually there are less graphics and extraneous information on mobile sites, but you should always include the option for mobile visitors to choose to view the full site.
Don't fall for some of the cons out there now, where developers market "mobile apps" which are in reality mobile websites; the technology and price are vastly different, and unscrupulous developers will charge you at rates for apps when they're just developing mobiles sites. Mobile sites are developed with the same technology as any other sites, the difference being that the site has the ability to detect whether it's being accessed with a mobile device, and if so, the server will display the mobile version. Special software is required to develop mobile apps, the languages used are generally different from the languages used in websites, and apps must be developed specifically for the type of mobile device they will be installed on. There are far fewer mobile app developers than there are mobile site developers, and all of this translates into a higher cost for mobile apps than for mobile sites.
While we're talking about mobile websites, it's important to note that Flash files can't be played on iPhones and iPads, so if you have a site built solely in Flash you're out of luck. I'm constantly surprised at how many major corporations still have Flash sites with no mobile alternative; this is crazy! If you insist on having a Flash site, you MUST have a mobile alternative or you're wasting your time and money; as an every increasing percentage of internet users migrate to mobile technology the number of visitors who will find your site totally inaccessible to them is constantly increasing.
Bottom line: work with a developer that you trust to make sure that you get what you're paying for and that the product that's being developed for you will meet the needs of your market. If you're working with an honest developer you won't need to know all the right questions to ask to get the right answers - the developer will anticipate various scenarios and will ask you the questions to ensure the final product meets your needs.