TC / Phone Different
You could run a webserver from the iPhone, and have it always be available at 127.0.0.1. There are also text editors in which you could store passwords, but they would not be as secure as SplashID -- they wouldn't be encrypted.
There are some decent implementations out there of web passwords, however -- for example, jkPassword.com supposedly just stores the encrypted values, not the actual passwords themselves.
Also, Agile Web Solutions is supposedly coming out with a web-based version of their 1passwd product.