Interfacing Arduino Uno with LG 420 GSM phone

Hi, I have an old prepaid LG-420 GSM phone I would like to use to send SMS messages from my Uno. I would like to use this phone instead of buying a GPRS shield, which is above my budget.

I am curious if anyone's had any luck interfacing an Arduino with a cell-phone? One idea may be to hack the keypad of the the phone and generate DTMF tones with the Uno to emulate keypresses, though I kind of doubt the phone uses DTMF internally. I could also wire each button of the phone to a D-O pin, but the Uno doesn't have enough I/O to do that.

The best thing I think is to control the phone via its USB port. Does anyone have any experience/suggestions on how to do this?

Here's one way to do it -> http://www.circuitsathome.com/mcu/programming/interfacing-arduino-to-a-cellular-phone , http://www.circuitsathome.com/mcu/interfacing-arduino-to-usb-gprs-modem

felis, thanks for the reply. This will work,but I'm trying to do this on the cheap, so I'm trying to interface the Uno directly with my existing phone, using the Uno's I/O pins to communicate via serial (or whatever protocol is required) over USB. I don't have a USB host shield, which is necessary for DealExtreme's device.

Unless this has already been done before, it may be more trouble than it's worth, and I may end up shelling out the $50 for a USB host shield and DealExtreme's GSM device. Or ... I may end up getting this: (since it'll end up costing the same, but will be more compact) http://www.diybin.com/products/Seeedstudio-GPRS-Shield.html

My original question is, can I interface the Uno using its I/O pins to speak Serial over USB? (without using a USB host shield, just cutting a USB cable and stripping its wires.) I realize that's exactly what the USB shield is designed for, but I'd prefer not to fork out the $25.

I think I found a way to control the phone without buying the USB shield. I'll wire up each button of the phone to be triggered by the Uno, using 4-bit BCD to talk to a BCD-to-decimal decoder. That way, I only use up 4 (+1 to turn on the decoder when pressing a button - otherwise, it will always be pressing the 0-key! - see truth-table) D-outs on the Uno to control up to 16 buttons on the phone. I'll wire each phone button to an output of the decoder, isolated by a solid-state relay. That way, when a decoder output goes high, it simply shorts out a button's contacts. I should be able to do it for about $10 versus $50. :)

Anyways, here's a schematic of my 4-bit BCD to hexadecimal decoder and a corresponding truth-table. http://www.prism.gatech.edu/~dschlender3/Files/GPS%20Tracker%20Project/BCD%20Decoder%20Circuit.png http://www.prism.gatech.edu/~dschlender3/Files/GPS%20Tracker%20Project/Dialer%20BCD%20to%20Hexadecimal%20Decoder%20Truth%20Table.pdf