I Have sim 900A uart modem previously I used this model for project to send sms with Arduino. Currently I am trying to use this sim 900A uart model in my latest project where I want to detect dtmf tones but as far as I can see in the documentation there is no command to detect dtmf tones but to there is command to generate dtmf tones.
Is it possible to detecting dtmf tone in this model (sim 900a uart). Or I have to buy another device for this or I need to update framework of sim900a if so then how. How can I detect the current framework version.
Can I use 4g sim with this model as I only tested it with 2g till now?