These are listed as 315 MHz but I received a 433 MHz module.
Range is not great but works for simple experimentation.
To transmit data, a Manchester encoding must be used. Manchester has no DC bias, so it's perfect for RF transmission. The encoding encodes the two binary states as a low to high or high to low transition. Another benefit of this is that it makes the encoding self-clocking.
Receiver has automatic gain control (AGC). When nothing is transmitting, the gain scales up generating a lot of amplified noise. When a transmitter starts sending, the high gain rails the amplifier. Transmit a preamble with alternating 1's and 0's to allow the AGC to adapt to the received power level before tranmitting real data.
I don't think the ESP-05 is able to be flashed; the appropriate pin is not available on the header. You need to ground GPIO0 to flash the firmware.
As of Fall, 2015, the stock firmware did not allow placing the ESP8266 into promiscuous mode, to capture all 802.11 activity, which was my original intent for this module.
470 uF cap across power supply helps on module boot. Range was excellent with the external antenna mounted to a window.
You can communicate with this module using minicom, but you need to disbale the serial port console login.