To retrieve your legacy MMS, please go to http://mms.saunalahti.fi/mms.
You’ll presented similar with the above picture.
What you need to provide is only your mobile number and password.
Read the received multimedia messages, log into the service.
Quote from Wikipedia:
In addition to ADSL and mobile phone service, Saunalahti also offers Finnish users Voice over IP without a monthly fee. The service includes free calls to Saunalahti mobile numbers.
Saunalahti doesn’t operate its own cellular network and thus relies on Elisa network. Saunalahti offers various mobile plans, most of which are cheaper than the ones offered by the parent company Elisa.