Personal VOIP

[Kiril]

I live abroad. Let's say I live abroad and I have an A20 server in my home country. There are a few modules for attaching a sim card to A20 like:
MOD-USB3G
MOD-GSM
MOD-GSM-B
MOD-GSM-EDGE
I am interested can I add a gsm module on the server in my home country and use it to call my friends? Is there a tutorial about this somewhere?
My second question is can I use 2 such servers with gsm modules - where I live and in my home country to be able to call my my friends through my phone from abroad, over the internet.
I am sure this could be done, but I have no idea how exactly it should be done, so I will be grateful if you can point me to a tutorial or something.
PS: I don't know if this is the right place for this post.

[KNK]

Similar question was asked before, so try to search for it.
There are very few GSM modules supporting voice and are not easy to find. Then, it will not be so easy to do what you want, but it's possible.
Much easier for you will be to use a VoIP provider and use your internet connection (at home or on your mobile) to call your friends ... PM me if interested.

[apollo]

take a look to this,you can port this from rpi to olinuxino
https://www.adafruit.com/blog/2013/04/12/raspberry-pi-gsm-gateway-piday-raspberrypi-raspberry_pi/

[dave-at-axon]

If you can run Android on it, then this is free and all source supplied so you can modify this to do what want, assuming you can programme Android that is.

https://code.google.com/p/sipdroid/