Make a sipmle microcontroller that will send its Serial Number to a smartPhone

There are cheap bluetooth modules all over ebay, you get one of those and simply interface it with the micro... Once that's done you pair it with the phone and send you info... Of course it's more involved overall, you need to actually write the code on both the micro and the phone to do the communications...

 

To write the code for the micro you will first need to pick a micro and then choose your development suite to write the code... There are a TON of compilers out there for most micros, you have to simply choose one that works for you... I would personally stick to Atmel AVR or Microchip PIC as they both have a huge market share and thus a huge number of options and support...

From that point you can almost always find example code that can be tweaked to work, until you get good enough to write your own code from scratch...

For example here is an entire tutorial devoted to getting an Arduino and Bluetooth module to work together....

http://www.arduino.cc/playground/Learning/Tutorial01