Hi Everyone!
I am trying to build a small gps tracker, the one that reply to an sms with an sms with the coordinates.
now, my question is: where can i find such a small gsm module for arduino?? (I was planning to use arduino nano or micro)
Do you know how to wire an embedded gps/gsm module to an arduino board?
Do you have any suggestion for this foolish project?
The piece should be max 18 x 18 x ... mm
18 x 18 x - Feet, inches, millimetres, decametres?
sorry, edit
Smallest I have come across is the SIM808, GSM/GPRS/GPS all in one but the chip alone is 25mm x 25mm.
Hi,
You will be very lucky to find one that small.
Don't forget they need an antenna, and the ones with built in antennas that perform properly are not that small.
Plus you need a radio module to tx and a controller to connect them and a power source.
You might have to see what you can get and then try for a minimal size.
Tom.... 
Do you know of something already built with that features?
If you Google 'SIM808', or 'SIM800' if you don't want the complexity of GPS built in, you can see what is available.
I agree with the others. Build something that works, first. Then, figure out how to make it small.
What are you trying to (unobtrusively) track, anyway?
I'm trying to track my bicycle. in case of theft
If you could make a very small Ruhmkorff coil, you might not have to worry about tracking your bike, because no-one would want to steal it in the first place!
u-blox guys manufacture a pretty small and supposedly low power GSM/GPRS unit here>> https://www.u-blox.com/en/product/leon-g1 (or search for more yourself!), mBed offers a development board with ublox GSM/GPRS module on it (not sure if it has the one I gave you the link of!) but goto their site and have a look.