HC06 are popular Bluetooth to Serial modules bases at CSR BC04 Bluetooth technology. They have with build-in 2.4GHz antenna, support Bluetooth class 2 power level and operate with voltage in range 3.1V~4.2V
If you want to add Bluetooth wireless connectivity to your next device without hassle with Bluetooth protocol, HC06 will allow you this working as simple as with UART. The module have AT commands to listen and pair to other nearby BT devices, then you exchange data like if you worked with wired uart.
Tons of Arduino examples are available on the net. The module is made to be easy soldered on your own custom board.
olimex 
Aug 28, 2015 @ 21:46:35
Will you also offer solderless versions of these, i. e., with pins?
Aug 31, 2015 @ 10:22:20
It would be great if the module could be certified by Bluetooth SIG as a compliant plug-in. If not so we cannot use it for commercial products, because BSIG is chasing everybody who uses uncertified modules.
Aug 31, 2015 @ 11:08:31
In case someone is wondering (like me), the supported version of Bluetooth is “Bluetooth v2.1 + EDR”
Sep 01, 2015 @ 16:28:46
Does it support BLE?
Sep 01, 2015 @ 17:25:33
no
Sep 18, 2015 @ 13:59:48
would it be possible to have alternative firmwares for file transfers (obex)?