SMS tickets are now valid also on route 57 in Helsinki.
SMS tickets are valid on trams, the Metro, Suomenlinna ferry, commuter trains within Helsinki as well as on eastern Metro feeder routes 15, 57 80-99 (also A, K, B, V but not on routes 90A and 91 or N services) and trunk route 560 within Helsinki.
You can also buy single tickets with HSL Mobile ticket app. Mobile ticket is a single ticket valid on all modes of transport. There are tickets for all HSL travel zones. Helsinki internal mobile and SMS single tickets cost €2.90.
Read more here.