Noise with Ring Indicator

hello,

i am using a SIM900 board connected to an Arduino UNO.



My goal is to react doing something upon an incoming SMS. To do so, i am using an interrupt associated to the RI pin.



Indeed, an incoming SMS triggers once the interrupt.

My problem is that also any AT command triggers the RI, several times for each command.



Any hint?



Thanks a lot

Mirco