Hello guys,
i need an advice from more experienced users. I cant solve the problem with my UNO and Sim900 module. Everything forks fine sendind/recieving SMS, i can make a call from Arduino to my cell phone. The problem is, that I cant call back. In the point of fact I cant make a call to the Arduino at all. When I try to dial the number of SIM in the SIM900 i can only hear that the number doest exist(3 tones).
When I remove the SIM card from the SIM900 module and put it to my cell phone, then everything is fine. Any ideas what could be wrong?
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so u want to recieve that call right ? Can u post AT debug?
AT datasheet: https://www.espruino.com/datasheets/SIM900_AT.pdf
ATA for receive call..
I would like to recieve a call. The problem is that the call refused to connect. So there is no Ring message in etc. in serial monitor. I`ve already tried to replace the SIM card for new one and the new one is working properly. So it seems to be a problem of the SIM card... but its wierd
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Similarly, I use a sim7600 for 4G i use one sim that never connects to the internet. One SIM card connects to the net but if I do call it disconnects and sometimes connects. another one works perfectly called the Internet both good in connectivity.
Strange things are happening 
But I would like to know what the problem is, because the faulty SIM card in the phone is working properly.
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sorry for late reply! i asked simcom they tell me it not support concurrency.. so after hangup call i do reset module if internet not get connect again. this solve issue for one sim..
Again on some sim if it connect 2g it uses less ampere power but when connect to LTE uses more so powering with laptop supply not good. It connect at start but after sometime again loose network. so good supply.. Also Checking that area have the network with supported band of network with that module.
The sim that not connecting not at all works only on VOLTE mode so gsm module with VOLTE is needed. But again this module not work as mobile phone we expect..
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