Dual use 3G Modem

Using Arduino Project Guidance
1

Hey guys,
I'm planning to create a carputer system, and part of this would include an Arduino for remotely turning on the computer/car via SMS.
Another feature I would like to include is internet on the go, hence I will be using a USB 3G modem with the carputer. In an ideal world, I would be able to connect the Arduino to the serial lines of such a modem and listen in for any text messages, and also be able to surf the net using the USB connection to the computer, but having searched around, the only options I seem to have are:

  1. Using a 3G modem for the computer as well as a separate GSM module for the Arduino (therefore requiring two numbers/modules/SIMs, not ideal).
  2. Using a basic GSM/GPRS modem with a USB-Serial converter, and tapping into the serial lines with the Arduino while the computer isn't using them (not ideal due to GPRS speeds).

Does anyone know of a 3G modem that has both a USB and serial interface, or does such a product not exist?

Thanks
Simon

2

The only reason I can see for needing the Arduino to interact with the modem is so that the Arduino can boot the PC in response to an SMS command. This means the Arduino and modem need to be running all the time anyway; wouldn't it be a lot easier to put all your internet related and SMS handling code on the PC and leave that running in some sort of low-power mode instead? It would avoid needing multiple modems or trying to share the modem between devices.

3

The issue here is power usage; even when idle, the board I'm using consumes quite a few watts, and as this is going to be using the car's battery it'll end up draining it a lot quicker than say, a fully powered Arduino.