Connecting to external chip (device)
For a beginner I would suggest Arduino - A company in china has just created a cool and cheap x-bee compatible device that has an ATMega chip (compatible with Arduino IDE) and Bluetooth in a single PCB called the Bluetooth Bee with Arduino. And here is a schematic.




  Description
  Save that extra Arduino you have lying around for another project,
  this two-for-one device has the Arduino built-in.  Bluetooth Bee with
  Arduino is an enhanced version of the Bluetooth Bee.  We added an
  onboard ATMEGA168 to it to make it a full-featured Arduino while
  maintaining the same footprint and instruction set as the Bluetooth
  Bee.  Plus, it still allows you to stack it on XBee Carrier,  XBee®
  Shield, and UartSBee for expansion or reprogramming




You can also buy the original development board from Arduino that allows you access to more input and output pins.




  The Arduino BT is a microcontroller board originally was based on the
  ATmega168, but now is supplied with the 328. and the
  Bluegiga WT11 bluetooth module. It
  supports wireless serial communication over bluetooth (but is not
  compatible with Bluetooth headsets or other audio devices). It has 14
  digital input/output pins (of which 6 can be used as PWM outputs and
  one can be used to reset the WT11 module), 6 analog inputs, a 16 MHz
  crystal oscillator, screw terminals for power, an ICSP header, and a
  reset button.




You pair to the device and you will get a transparent communications port where you can send and receive plain text messages. Thanks to this it is easy to develop code for both devices because they already have libraries to help you.(except iPhone and WP7- So that leaves Android and WP8 (possibly iPhone5))

You will still need other circuits to control your devices so you should do some more reseach into what you will need. The Arduino(or similar MCU's) simply cannot switch or drive heavy equipment.