When I was travelling a decade ago I needed a way for friends and family to be able to contact me. Roaming rates were ridiculous at the time (something like £3/

When I was travelling a decade ago I needed a way for friends and family to be able to contact me. Roaming rates were ridiculous at the time (something like £3/min to receive calls). As such I got a local prepay SIM card in each country I visited, however sometimes I only had a number for a week or two before I went somewhere else, so giving that out to people wasn't a good idea. I got a VOIP number in my home country, and set up my mobile number (at home) to redirect to that - this is a feature of GSM, so should be supported nearly everywhere. *21*<destination number># to activate it. My home number was just calling another local number, so it was included in my plan. I setup the VOIP number to forward to the SIM in the country, and every time I went somewhere new I just changed the destination number. So I was reachable, and only had to pay a few pence per minute for it. That mostly worked, but when someone called me it showed my VOIP number, not the number of the person who originally called. In Asterisk I could see I was receiving the caller's phone number, but my SIP trunk provider was filtering it out. One little email to support and I was able to set the originating number so it showed who actually called me - in reality this meant I could call anyone worldwide with any originator number shown. The other problem which goes with this article is how to make outgoing calls. At first I used a SIP client on my computer, but then I went to a few places with pretty poor internet so that wasn't possible. I setup a script on Asterisk so if it received a phone call from my number (of the local SIM I had at the time) it would reject the call, then after a few seconds call me back. It would present a dial tone, and allow me to enter a phone number to call, after which it would dial it and connect me. Technically someone could have spoofed that, and made phone calls at my expense, but I figured the risk was pretty low. Boom, ultra low cost international calls while travelling :-)