International roaming costs are too high? Raspberry Pi SIP-GSM design to help you

March 18, 2023

If you travel a lot, are you used to the unreasonable mobile roaming charges? However, mobile phones are sometimes absolutely necessary – we have to pay for mobile roaming when we work or go overseas, because we need to stay in touch with the office and talk to people around the world about the Raspberry Pi.

Holger Leusch, Benjamin Reichel and Karina Hochstein all face this problem. To make matters worse, Holger often goes to Cambodia, but his German mobile phone supplier doesn't even have any roaming agreements with Cambodian telecom operators, so he can't continue to use the original mobile phone. Cambodia’s reluctant call quality, disgusting bandwidth, delays and disconnections made him unbearable. The reality is that he, like us, needs to keep in touch with the office.

Go into the realm of the Raspberry Pi:

Many people put themselves in the ground and might consider buying a SIP-GSM-based gateway. However, the GSM gateway is not cheap: Holger research found that a single GSM gateway (you definitely need 2, 1 gateway for each location), priced between 200 and 400 euros. If you invest such a high price, how many calls can you make it? Therefore, the three of them did their own, and the final choices included: running RasPBX through Raspberry Pi, Huawei 3G wireless network card, Asterisk Huawei 3G wireless network card driver, and USB mode conversion tool. The full set is worth about 75 Euros.

Holger said:

Now, when someone calls my GSM number in Germany in Europe, first my mobile phone in my country will ring, and after 5 seconds, I will transfer it to my Cambodian mobile phone. As a by-product, from now on, my Cambodian friend can call my Cambodian mobile phone and finally make a call or text message with my German mobile phone. The call charge is very cheap...

Over 10,000 kilometers, the quality of the connection between the two gateways 64 kbps Asterisk "SIP trunk" relay technology is really great, and the people I talked to didn't even notice that I was overseas. It should be noted that the UK's communications authority, Ofcom, said that in some countries, the telecommunications laws associated with GSM gateways are still vague:

Ofcom recently clarified that under UK law, it is perfectly legal for users (whether corporate or general) to purchase, install and use a GSM gateway as long as they use it themselves. However, no one should use GSM gateway devices to provide communication services to other individuals, organizations or businesses, otherwise it will be illegal regardless of the geographical location of the gateway device or the number of end users connected to each gateway. This "commercial" use ban applies equally to mobile network operators (MNOs) and other organizations, as mobile operators' current licenses have not been extended to the installation and use of GSM gateways.

Basically, you can build your own gateway in the UK - but if you try to sell or rent this service, you will be miserable. However, if you want to use this method to save roaming charges, mobile network operators sometimes take further action. For example, if a mobile operator suspects that you are using a SIM card for a GSM gateway, the carrier may deactivate the card. Therefore, it is important to carefully study local regulations before taking this action.

ofGEEK:

RasPBX is a complete installation tool for Asterisk and FreePBX running on the Raspberry Pi.

PBX (Private Branch Exchange) User Level Switch

Asterisk is an open source software VoIP PBX system. It is a software-only implementation running under the Linux environment. It is a very full-featured application that provides many telecom functions to turn your x86 machine into Your own switch can also be used as an enterprise-class commercial switch.

FreePBX is one of the most powerful GUI (web-based) tools for configuring Asterisk. It provides everything a standard traditional phone system can do, adding a host of new features. Formerly known as Asterisk Management Portal, FreePBX is a standardized implementation of the IP telephony tool Asterisk, which provides a web configuration interface and other tools.

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