In the year 2005 I started to write software for mobile phones. That was long before the iPhone. These apps use a technology called J2ME (Java Mobile Edition). Some of my apps are less than 100kb big, so they worked even on low cost phones.
You can still access information about this software on these pages.
If you have a compatible phone, you can even install these apps. Unfortunately, the official stores are of that time are no longer available (Nokia Story, Sony-Ericsson Store, Vodafone Betavine, etc.)