Perhaps it has been posted elsewhere, but there's a story on /. which implies that shell access to the iPhone has been achieved adapting a serial port to the dock connector.
http://it.slashdot.org/it/07/07/07/0249211.shtml
B
http://it.slashdot.org/it/07/07/07/0249211.shtml
"A team of researchers dedicated to finding means to fully control and interact with the new Apple iPhone claim to have successfully gained an interactive shell on the device. In order to achieve this feat physical access to the phone is required, as it relies on some minor electronics to be created and connected to the phone's serial port. It is believed that general control over the iPhone will be available to the enterprising researchers within a week (after all, it has only just been a week since the iPhone was released), with the promise of enough control to allow for self-propagating code not very far away."
B