olemus
modemi juhtimise käsk,
algab tähepaariga AT (< attention, "tähelepanu")
=
a type of instructions used to control a modem

ülevaateid
https://en.wikipedia.org/wiki/Hayes_command_set

http://www.codeproject.com/Articles/85636/Introduction-to-AT-commands-and-its-uses

http://www.developershome.com/sms/atCommandsIntro.asp

http://www.smssolutions.net/tutorials/gsm/sendsmsat/

https://docs.rs-online.com/5931/0900766b80bec52c.pdf

https://www.sparkfun.com/datasheets/Cellular%20Modules/AT_Commands_Reference_Guide_r0.pdf