To Ämtö you can easily get to either the Archipelago Line or the Archipelago Traffic.
The Archipelago Line (Green Line) runs every day of the week from Fyrudden to Ämtö and is run by the Archipelago Company. Book online at: www.skargardslinjen.com
The archipelago traffic runs weekdays and is run by Östgötatrafiken. Then the trip is booked on +46 771-711020 (no later than 18.00 the day before).