I need a similar application, whereby I may call from my mobile to the local #, which then connects me to overseas local #. I found the cheapest harware is about $220 each. You will need two of them, one at each end.
check this out:
http://www.puredata.com/products/ip_telephony/sip.htm
I have not installed it yet. But this is closest I found to my application. Another option is to setup two linux Asterisk PBX systems at each end. It is a little more complicated but robust application platform for tech-savvy dudes. I am not.