I want to mention one more thing, I don't know if it's in the x-payments connector, if not it can be addressed separately, but if it is then maybe a fix could be worked into this update.
I had my address in the address book with phone number.
After placing an order, at some point a copy of that address book entry gets created, without the phone number
http://www.signtorch.com/bin/xcart/addressbook.png
in subsequent visits to checkout, it uses that copy to fill in the address fields, which causes the submit button to be disabled, and that missing phone number is not very obvious or expected from the customer standpoint, so it can be hard to figure out what to do to place the order.
whenever that copy is made, it needs to also copy the phone number
or better yet, don't even create a copy in the address book like that
ultimately the missing phone number just blends in with the page, and is hard to spot, by anyone not expecting their phone number to be missing
http://www.signtorch.com/bin/xcart/checkout.png