Control external circuits?

Hi,

I want to find a way of controlling things like motors from my phone.

I basically want to dabble with robotics, combine the phone with a model RC car, using the phone for its sensors and a to controller the motors.

The problem, I can't think of a good, simple way of getting data to/from the phone.

Options:
1) Use Bluetooth. this would need a bluetooth PIC module or similar, ($60), and some seriously difficult programming. (As if android wasn't bad enough). The bluetooth module would control the motors.
2) Wifi, as above.
3) Use the phone's flashlight to send serially encoded signals. (This would have an appauling bandwidth, reliability and efficiency)
4) Audio - connect the phone's headphone jack output to a circuit that detects tones at certain frequencies, and uses that to trigger the motors.
5) Erm, that's all I can think of.

It seems the audio option could be the simplest, but it seems like one hell of a hack!! Anyone done anything like this with their phone?

EDIT!!

It's just occurred to me that there are bluetooth/rs232 converter modules for just $5 on ebay, so I'll pick one of those up and see if I can interface with it. It's not much simpler tho, it seems I'd still need to program the unit via rs232, I suppose I could program it using the PC, then transfer it to the robot's circuits, but wow, this is hassle, I'd have thought there would be plenty of robotics fanatics out there for there to be something quick and easy that takes advantage of these amazing phones!!

 

I've seen some little wifi modules, even with a built in web server, but they were about $60 or more. Very cool little things! I'd use one of those, but there are so many benefits to using a phone with all its sensors etc, it would be nice if the interfacing circuitry was minimal.