I find the sendmycall site quite confusing, but I hope this will work:
1. Get a free "IP Freedom" account at Callcentric. Set it up as SP2 on your OBi. If you have trouble getting it to register, search this forum for help, or post a specific question.
2. Test outbound, by dialing **217771234567 from the phone connected to the OBi. You should hear the TellMe prompt.
3. Test inbound, by calling 1-646-810-9280 (or another SIPBroker PSTN number) from your cell phone. At the prompt, enter *4621777xxxxxxx (replace xxxxxxx with the last 7 digits of your Callcentric number). Your OBi phone should ring; answer it and confirm that you have audio both ways.
4. On sendmycall, set forwarding destination: VoIP, Protocol: SIP, Host:
in.callcentric.com, Account: 1777xxxxxxx (your Callcentric number).
5. Call your Argentina DID and confirm that it works.
IMO, any solution involving Google will either cost you per call, or be more complex and less reliable.