wvmarle:
So one complete phone + 1 Bluetooth module that works with the Arduino to communicate with the phone is cheaper than that just a 4G module!
Dead right...
The first smartphone I got was a $AU49 Huawei bought specifically so that I could use Bluetooth Graphics Terminal with a Mega+HC-06. That was the combination made in heaven. The SIM stayed in the dumbphone for quite some time because I didn't have a car cradle for the new one. Besides, the Huawei offered no advantages as a phone - indeed, quite the opposite.
I think the local 2G service was shut down in 2012, and I have been waiting to see somebody use a real phone connected to Arduino via USB cable ever since. I'm surprised 2G is still available anywhere these days. Apparently it is, but maybe not for long.