I’ve a project where I’d like to power the LoNet Mini GSM via an ac/dc converter (“wallwart” power supply) and variable voltage regulator within my circuit. I’ve created this circuit and tested the voltage which is pretty steady at 4V. Also the converter powers via separate 5V regulator a 5V circuit. I plugged the Mini GSM’s VCC to 4V, the GSM’s VIO to 5V, GSM’s GND to common ground, tx to arduino’s RX and Rx to arduino’s tx… and the unit powers up just fine. However, the GSM does not output any information on the TX (I.E. does not echo any information on my Arduino IDE Serial screen) from any “AT” commands. With an oscilloscope, I was able to confirm that the GSM is getting the proper signal on the RX, but the TX remains silent (no signal). Finally, I can confirm that the GSM is understanding the “AT” commands sent as I am able to power the unit off with a “AT+CPOWD=1” command. Please help! 
…as a note, when I say I connect the TX and RX lines to my Arduino Uno, I’m using pins 10 and 11 and softwareserial as demonstrated in the GSM’s documentation.