Raspberry PI continues to surprise us with the low cost solutions we can build by our own.
This time I have a PBX solution to avoid roaming costs between our office in Brasil and our headquarters in Portugal. This solution also works when people are traveling around europe (very usual) too.
So, basically I have a Raspberry PI running Asterisk and configured as a public PBX (security issues had been taken). I also have a Huawei E180 GSM modem to route outside or inside calls to landline or mobile phones or even internal extensions.
So, when people are traveling, they just open their favourite application for Android or iPhone trough wireless or 3G and call the desired number. The call is routed (free) trough internet and the raspberry just forward the call trough the GSM modem. So, the call is completly free because we have thousands of free minutes to use in our rate contrat.