I am a developer for http://www.gomadic.com we just completed a universal device that allows you to connect your cell phone to a PDA/Laptop and dial into the internet called the ComCube.
Here is where it gets fun. I have been using it for my IO in my car!!!!! Without having to convert from TTL to true RS232. But if you already added the converter for your TTL RS232 in your IO then you can still use it. Here is the secrete:
Just buy the cell phone to Laptop combination at http://www.gomadic.com and if you have a PDA then pick one of those up too. If you have the True RS232 on your IO then just plug in the 9pin connector. YOU NEED RTS PIN 7 TO POWER THE CIRCUIT, OR CONNECT 5V TO THIS PIN
If you don't have the RS232 converter then here is the pinout to use the connection to your cell phone via TTL from the IO. Just by the end for the VISOR and cut off the VISOR connector then connect the following pins to your IO.
Connect your IO to the RJ45 Pin
8 connected to TTL RX on the phone so connect your IO TX here.
7 connected to TTL TX on the phone so connect your IO RX here.
6 Connect your IO GND here.
5 - Reserved
4 CKT PWR (3.3V to 12v or RTS signal)
3 True RS232 9pin RX
2 True RS232 9pin TX
Where Plug Pinout is:
Better yet feel free to use these as a converter. The TTL TX pin 7 will be converted to RS232 RX pin 3 and RS232 TX pin 2 will be converted to TTL RX pin 9. Be sure that the Circuit has power via pin 4.
Gomadic doesnt support "hacking" the ComCube but email me if you have questions.