Check out this discussion about a Raspberry Pi GSM gateway project over at RaspberryPi.org:
If you travel a lot, you’ll be used to absurd roaming charges when you use your mobile phone. But sometimes your phone’s an absolute necessity – those of us at the Foundation can’t really go overseas for work or for holiday without paying those charges, because we need to be in touch with the office and with a lot of other people around the world who need to talk about things Pi. (And we like to be able to phone our mothers.)
Holger Leusch, Benjamin Reichel and Karina Hochstein have found themselves with a similar problem. Worse still, Holger travels to Cambodia a lot, and his German phone provider doesn’t even have a roaming agreement with any of the Cambodian telcos, so he’s not able to use his phone there at all. He found VoIP unusable in Cambodia, with patchy calls, lousy bandwidth, delays and dropouts. Like us, he needed to be in constant touch with his office.
Enter (you knew this was coming, didn’t you?) the Pi.
Many of those in Holger’s position would look into buying a SIP-based GSM gateway. GSM gateways are expensive things: Holger’s research found that a single GSM port (and you’ll need two, one at each end) was priced between €200 and €400. “For this to pay off, I would have to make a whole lot of phonecalls.” So he, Benjamin and Karina built their own, using a Pi running RasPBX; a Huawei dongle for 3G; a Chan dongle which works as an Asterisk channel driver; and a USB modeswitch. The whole kit came to €75.
Now when a caller in Europe calls my german GSM number, first my domestic Snom phone rings, then after 5 seconds, my Cambodian mobile phone gets called. As a sideffect, my Cambodian friends from now on can call and SMS my German phone back at local rates of a few cents…
The connection quality over the 10.000 km spanning 64 kbps Asterisk SIP trunk between both gateways actually is so amazing that none of the callers even noticed that I was out of the country at the time! ….
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