Epoch seems to be a pretty complete payment solution with recurring billing, foreign currencies, etc. already included. But they are very expensive, with a $500 / $1000 deposit for selling digital products and high transaction fees starting at 15% of every sale. It is probably not something we would pursue as very few customers would want to pay those rates, but we will leave this request open to see if there's more interest.
You might approach them and see if they can use our open API to push purchase and contact information back into ONTRAPORT. Because they are a complete billing platform you might be able to do this and use ONTRAPORT for the automated marketing portion and Epoch for the billing / accounting end of things. This might be the better solution, especially if you are using their currency conversion features (ONTRAPORT does not have any currency conversion features to adjust sales volume for different currency values.)