Hi S.,
As a person who was adopted as a kid, and did have a few meetings with my bio dad when I was about this age, let me suggest talking to someone like a counselor before you even start with Skyping and phone calls.
This is very, very hard to explain to a child. I personally think that you and your husband need to sit down with someone and talk about this before starting with this communication. Your husband is her Daddy, and maybe it would be helpful to refer to her father as 'her father', when the time is right.
At her age, however, this is confusing, because of a lack of understanding about human biology. I want to add that I have concern and empathy for your husband-- so do take care of him. This must be difficult to have this other person from your past becoming more present and wanting contact with the child he is raising. Is her bio father paying child support? This should also be considered.
Please tread cautiously in going forward with this. If her bio dad has had this change of heart, that's great, but what if he doesn't want to stick around? What then? It's just so abstract, which is why I suggest talking to a family counselor who can help support everyone through this time. I truly hope this all works out well for all of your family.
And I agree with Diane B-- checking out where this all sits, legally, would be good if you have any concerns at all about starting contact.