Translation:Communication between husband and wife is important.
Well, the order is different and I'm not sure if it's even correct in English. In Polish it would be "Komunikacja jest ważna pomiędzy żoną a mężem" and I'm also not sure about its correctness...
"i" is accepted, should be fine.
And I was thinking about sentences where both 'a' and 'i' could work exactly this morning... :)