PayPal can be used internationally, but it has some caveats. Simple recurring billing works quite well, except that you have no control over the subscription.

PayPal can be used internationally, but it has some caveats. Simple recurring billing works quite well, except that you have no control over the subscription. Only thing you can do is to cancel it via PayPal interface. Multiple plans become quickly painful. There's also Adaptive Payments API, which is available for non-US companies. PayPal doesn't really trust you: subscriptions are limited to one year in length, but you have the control of when and how much is billed (within limits of the "preapproval"). Adaptive Payments API is quite painful to use and is challenging from UX point of view. It's probably cheaper to incorporate in the US and use some other merchant gateway than to implement PayPal Adaptive Payments in your software.