No need for an apology - though I do appreciate the effort to make it. :)
Grins - yes, written communication is certainly a task we all get better with over time. Practise makes perfect (or better, or something like that..)
Okay, fantastic! - now your intentions are crystal-clear. I thought it was possible that you may have wanted to do something like that, though didn't want to guess and make wild assumptions.
I think that this project is a real 'doosie' and one that even a seasoned hardware-hacker would find very challenging..
I hope my questions earlier didn't give the impression that I necessarily had a solution for any of them..
You might be able to find some documents that discuss the specs of the GSM stack (I think its called that) which is the low-level part of the circuitry that decodes the data sent. You may be able to solder wires to the correct pins and use some logic gates as a decoder to look for specific inputs - perhaps with the aid of a small micro-controller, you could intercept the contents of those text messages to extract textual commands from them? I really don't know - I studied digital systems, robotics, etc at college, mobile phones were quite rare (and HUGE) back then - we certainly never had them.
Something else to consider is that many alarm systems have cellular-network connectivity (like newer Coke machines), you can configure some to send a text message if activity is detected. _Perhaps_ these modules are ubiquitous enough that you could find a forum of hardware DIYers that have used such a module to report activity from/control an alarm.
I was there around the time that the change from discrete parts to integrated solutions was less complete, and you could still find an EPROM (complete with erase window) inside many items (max 65,536 bytes!) - I even de-soldered many parts from ircuit boards to use in our lab classes.
The reason I mention all of this, is that today (and for about 20 years) mobile phones have been mostly integrated systems - many different loosely related functions are done in single chips - you wont even get access to a pin or a wire for much of the data they consume and create. Accessing the data may quite possibly be most easily done with (a) a robot with a finger to press buttons to enter it, or a robot with a video camera and a finger to navigate through and access the data. The circuits inside the phones operate at quite high frequencies (Many Mhz, or even Ghz) - it's not terribly easy to find a digital sampling CRO to examine these circuits with, for little money.
Likewise, with the GPS unit - that is something I would still be moderately hopefull could be re-purposed, but finding a data sheet may be very, very tough. BUT there is a big DIY following for finding alternate uses for the screens from Nokia 3310 and 5510 phones. Perhaps there is a DIY gps hacking community too?
To be honest, I would probably consider trying to do the project with off-the-shelf components that I then fashioned into a complete system.
You can buy GPS tracking units for about $35 - perhaps this is cheap enough to be worth playing with for you. BUT while the receiver unit is quite cheap, I'm not aware of the method that the companies selling them use to report the devices location back to you, the user is. They seem about the size of a 3G internet stick, so perhaps they send the data back that way - which is why you have to pay a monthly fee.
But, if you could read the positional data from it yourself, there's nothing stopping you from using a radio to transmit the data you read from it. Perhaps a pair of cheap CB radios (5km range, ~$30/pair) would be sufficient for that - you'[d still have to modulate the data yourself though - a $10 arduino board would do it just fine.
Incidently, you could control the stepper motor from any controller that had a couple of inputs and outputs, you could use the same one to modulate your transmitted data and control the stepper motor.
I apologise, I realize that this post speaks of just about everything except the GSM network - but that's the problem with today's manufacturing processes - everything is integrated and increasingly difficult to re-purpose effectively - hence the video-camera/robot references.
It seems unlikely to be what you're really after, though I do note that you can get very cheap video camera, ($9 for a pcb mount unit!) gps and logging units these days. The FirstPersonView (FPV) market of RC planes has brought the price of some of these units down substantially. It would allow you to construct a working system, though it would rob you of the learning experience of working through all the nitty, gritty details. It would also rob you of a major part of the satisfaction too. :(
Kudos for tackling such an ambitious project! Hope you can connect with the right people. :)
Here's a couple of links that _may_(?) be of interest:
Telemetry (gps + assorted) items
FPV accesories - goggles, video transmitters, etc, etc