How about HiJack?
It will open new ways to connect iphone with lot of embedded systems.
Here’s a relevant project by SpiritPlumber, a $10 audio-to-serial cable that works with Android:
https://groups.google.com/group/cellbot … 764fb664dc
There’s also microbridge, a library that I wrote for interfacing Android phones with Arduino using Oleg’s USB host shield (http://www.sparkfun.com/products/9947).
http://code.google.com/p/microbridge/
The USB shield solution is a bit more expensive, but gives you bidirectional communication. Both should work on all stock, unrooted phones.
If you don’t mind jailbreaking your phone, here’s a good post about getting serial comms on your iPhone:
http://hcgilje.wordpress.com/2010/02/15 … unication/
If you own an HTC Android phone you can get serial comms from the ExtUSB connector (requires root afaik):
http://www.instructables.com/id/Android … ial-Cable/
If you don’t mind rooting your phone you can also enable host mode on some phones (i.e. ZTE Blade, Nexus One), which allows you to talk to a Teensy for example