executes at commands by intializing serila port parameters

短信的收发，这个代码和往常的不一样，大家可以通过这个代码学习一下-Send and receive text messages, this code and as usual we can learn about this code

Handle incoming SMSes. Just dispatches the work off to a Service.

This service essentially plays the role of a "worker thread", allowing us to store incoming messages to the database, update notifications, etc. without blocking the main thread that SmsReceiver runs on.