Looking at SIMCom support for the SIM800C I must admit that they impress. I had to register on their site and after that I have Access to 20 Application documents, AT commands, certification documentation and updated hardware design & user manual.
I have a dev-kit on it’s way + a module, also a devkit of the SIM800L.
This is the smallest of the modules I am looking at measuring only 17.6 x 15.7 mm. The hardware design guide is well documented With schematic examples and With 20 app notes that seems to have decent complexity and content this will be fun.
What I need now is antenna and SIM card holders etc for my Ethernet module. How I use the GSM is still an open question – it has a TCP/UDP Interface, but I wonder if SMS Messages are more cost optional – or maybe a mix.