I'm currently talking from my Android phone to an Arduino Uno using the BlueSmirf Silver from Sparkfun.com http://www.sparkfun.com/products/10269
. Talking from an iPhone requires MFI certification and a custom chip that only certified MFI partners have access to.
The BlueSmirf (which is really a just a Real Networks RN42 with a 3.3v regulator and some status LEDs) has the ability to be a master or slave and swap roles dynamically. I'm using basic serial communications, but it works at relatively high baud rates (I run 57,600 baud). Other profiles are supported if you are so inclined. The BlueSmirf board physically connects to the Uno with 4 wires (VCC, GND, Tx and Rx). It is really simple to get working. This should serve your purpose.
Three Arduino Unos, each with a BlueSmirf board attached can discover each other, pair, connect to one another, etc. using the time honored AT command set (from the modem days). If you want longer range, the BlueSmirf Gold (if memory serves) uses the RN41 which has a stronger (i.e. Bluetooth Type I) radio.