Do you already have a specific camera in mind for this solution? I remember reading about a GSM modem a while back, which had an integral camera. I don't remember whether it was an Arduino shield or a standalone board. It was controlled using an AT extended command set via a serial port and could be commanded to send an message containing an image captured from the camera. I seem to remember it could also send a video stream but may have misremembered that. If you track this camera/GSM modem down, it would make your project very easy. Alternatively find/write an app to do that on a smartphone or feature phone.