The iPhone client is actually capable of playing on existing Graal servers since iPhone accounts are essentially just special trial accounts that "never run out", however there are some limitations. Just to name a few:
- You're limited to on-screen controls, which need to be designed well, and also existing GUI windows with fiddly controls of any kind (scrollbars, list controls with thin rows, etc) need to be modified to be finger-friendly
- You always need to test on an older device so that some people aren't lagging when others are, and older devices have quite slow CPUs and don't cope well at all with clientside timeouts or heavy clientside scripting
- Certain functionality is missing (such as the built-in Q menu, the default PM system, a few script functions)
- People that use iPhones over GPRS/EDGE are going to be subject to a pretty latent and horrible connection; it will take them ages to log in and they'll be very laggy
If you have some specific project in mind then you can speak to me about it and something can maybe be sorted to allow testing on iPhone.