I connected everything – that is: battery, SIM card, push button, LED and transistor and level shifting for 2.8V <-> 5V logic. And considering how much trouble people seem to have had I was surprised how quickly it worked!
The only two things I ran into was:
- The first SIM card I used didn't want to talk to the GE865. Probably because it is for a 3G modem and not a phone. Anyway, the second (normal) SIM card worked perfectly.
- Using the Arduino IDE's serial monitor as terminal interface didn't really work. But using "screen /dev/tty.usbserial-A9007ND2 9600" from the Terminal prompt worked flawlessly.
I had zero problems with the power supply. Even though I'm not using the recommended low ESR capacitor. Maybe because I'm in a densly cell-phone-covered area. Or maybe because the battery is capable of delivering up to 2A by itself.
And everything worked: sending and receiving SMS'es, retrieving a web page using GPRS. Nice! Now I just need to connect it to a DTMF decoder and a Speakjet :-)
Here's a picture of the breadboard setup:
(click to view large version)