Trillian Astra is IM for iPhone
A version of the application, called Trillian Astra for iPhone will allow you to IM on the phone, which is a feature Apple didn’t put in the phone by default. Designed for the iPhone, the Astra uses the internet browser and as long as the window is opened, real-time messages will be delivered.
An Alpha version of the Trillian Astra will be available in few weeks, and if the tests run smooth, probably soon after that we will see a final release.
Source: Trillian Blogs via EngadgetMobile