Do the BT2S Bluetooth modules accept both 3.3V and 5V serial signals?
Is it actually rated for 3.3V and just happens to work with 5V or are there level-shifters used to ensure a 3.3V signal despite the input?
Is the power input regulated to 3.3V for the Bluetooth chip itself?
I am wanting to use this for a design project with the Teensy 2.0 (which can be set up for 3.3V but I am trying to keep 5V across the entire project for other reasons). Right now my design is using a couple N-Channel MOSFET level shifters using a similar module from Kootek (http://www.amazon.com/Kootek%C2%AE-Bluetooth-Serial-Module-Arduino/dp/B00DQ4A7O6/ref=cm_cd_al_qh_dp_t) but I would like to avoid stuffing SOT-23s if I can. The Kootek version of the BT2S states it can only take 3.3V for serial comm… There are so many of these out there and not a single schematic or useful datasheet :/
Though the Virtuabotix BT2S Slave and Master are VTTL (3.3 Volt) devices they have been successfully tested on several 5V systems to include the Arduino Uno, Arduino Mega, Arduino Due, Arduino Leonardo, Versalino Uno, Versalino Nano, Versalino FTDI, several PIC chips, and many other 5V systems.
The way you can tell if a particular device should work would be to look at the hysteresis and Voltage High (You want this to be no more than 3.0 Volts to be safe) of the microcontroller that will be processing the serial data. In the case of the Teensy 2.0 the ATMEGA32U4 is the same chipset family that the Arduino Leonardo is based on, and as such I would expect the Virtuabotix BT2S Slave and Virtuabotix BT2S Master to work on the board without issue.
Either way be sure to post back once you have tested it out so we can see if this was the case.