Not really currency rates. More the private settlement between national carriers which were a bilateral peering agreement, not unlike current peering/settlement between ISPs: neither party wants to give money but loves receiving money and in many respects, I am told the USG asked the bells to use this as a way to shovel money into developing economies worldwide: Unlike every other economy, the US had no single nationalised Public Telephone Company or PTT, so there was a wierd asymmetry around this process, US foreign policy, aide money.

By turning a blind eye to some rather odd call source and call sink behaviours, a lot of cash went from the US into the national telcos overseas. Where it went after that isn't entirely clear.