SIM Card
I obtained a “Mini” SIM from Rogers Wireless. They just call this size a “Regular” SIM (micro and nano being their other sizes). The current plan allows 10MB/month for $5 (but the SIM card costs $10!).
Board resets when antenna connected
This is a bit misleading and is in fact caused by a low battery or a battery unable to supply sufficient current. Communicating with a cell tower can draw a lot of power. With no antenna attached, no high-power transmissions were occurring, which is why this issue only presented when the antenna was attached. Either ensure that the battery is fully charged or is powered via USB.
Local Echo and Linefeed
TThhiiss is what happens when local echo is eennaabblleedd. Your terminal software may have a setting to disable it (Ctrl-A + E in minicom) or you can use the AT command: ATE0 (disable) or ATE1 (enable).
The SIM800 responds with a lot of carriage returns and linefeeds. In response to a simple “AT” command, it responds with <CR><LF>AT<CR><LF>, which seems a bit unnecessary. Disabling linefeeds in your terminal (Ctrl-A + A in minicom) can make things a little more readable.
Libraries, API
This device is aimed at microcontrollers and single-board computers. Adafruit has an Arduino Library and has instructions on adafruit.com for using TCP/IP over PPP on a Raspberry Pi and BeagleBone Black that use existing Linux software.
For simple applications, a full TCP/IP connection might not be necessary, or wanted if the aim is to keep data transmissions to a minimum to save bandwidth and/or power.
I created a Java library for the FONA that might be useful to someone.
In Practice
I built a complete solution using a FONA, BeagleBone Black, and Java. It worked, but needed a lot of “babysitting” to make sure the connection was available when it was needed. Using the FONA in “tethered” mode was more reliable, as the OS could manage the PPP connection automatically. With the cost of data plans falling all the time, the extra data transmitted really doesn’t make a difference to the budget.
When you add the price of the FONA to the extra complexity of wiring it up, it really is more efficient to use a $20 USB modem. It’s plug-and-play and can be replaced easily with an equivalent off-the-shelf part. I think I’d use a FONA in future projects only if I really needed to keep transmissions and/or power consuption to an absolute minimum.