If you only want to program the mobile phones for instance, then you'll need to deal with the operating system of the mobile phones. So you'll need C/C++/Objective C/Java/C# etc, that can be run on mobiles.
If you want to program the tracker, then you'll need to be able to program the firmware, which is usually in C/C++ or even lower-level hardware programming languages like VeriLog, or Assembly as you've mentioned.
On a high level, you might also need database programming to collect data for analysis.
The best way is to learn as you go. :)