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A few years ago I wrote a post about using an EC20 module with Asterisk and FreePBX for SMS forwarding and VoIP. The goal back then was to free a SIM card from an always-plugged-in old phone, so that it could make and receive calls through Asterisk and forward SMS through Telegram and similar tools. A few years later, I saw a seller clearing out first-generation DJI Enhanced Transmission modules on Pinduoduo, so I bought one for a little over 30 RMB. Its USB ID shows up as 2ca3:4006 DJI Technology Co., Ltd. Baiwang, but based on online information and its AT command responses, it is essentially an EG25/EC25-class Qualcomm-based modem. The catch is that it cannot be flashed with standard Quectel firmware. ...

In many parts of the world, mobile phone numbers are increasingly intertwined with online services and personal identity. This is particularly true in mainland China, where a single user may find themselves managing multiple phone numbers for various applications and platforms. While solutions like telegram-sms and SMS-forwarder have emerged to address the inconvenience of managing multiple physical SIM cards, they come with limitations. These apps, typically installed on smartphones, are often hampered by aggressive background process management common on Android devices, leading to unreliable SMS forwarding. Furthermore, the practice of keeping older devices powered on long-term for this purpose introduces safety concerns, such as battery swelling. Perhaps the most significant limitation is the inability to handle phone calls; these apps only address SMS. This article details a project where the author, using an EC20 cellular module and a blend of software tools like asterisk, to overcame these limitations. The setup allows for SMS messaging through instant messaging applications like Telegram, and makes and receives phone calls over the internet using SIP clients, providing a more robust and flexible solution. ...