Just send your payment in the return envelope included with your bill. Make sure you include payment form from your bill and write your account number on the memo line of your check.

Bill Payment Address
for ACS Local, Long Distance, and Internet:

ACS
PO Box 196666
Anchorage, AK 99519-6666

Bill payment for ACS Wireless:

Alaska Communications Systems
PO Box 92400
Anchorage, AK 99509-2400