So, each WML deck of cards must be small. As the WAP support for graphics is limited to small, static, monochrome images, do not use a graphic unless the service really benefits from it. Otherwise, you will be wasting time, bandwidth and user patience. You cannot rely on emulators to precisely reflect the behaviour of real handsets, so test the service with as many real handsets as you can acquire. So, when creating WAP services you must have a clear policy for supporting these diverse clients.
Security is more complex.
As there is a gateway between the handset and the WAP site, and as the two halves of the chain support different security standards, there is potential exposure here. Understand what type of secure access your gateway provides. Work with it. We have found the above principles to be both obvious and easy to follow. WAP services do present challenges.