Little report from my trip to Tallinn:
Elisa SIMs indeed very widely distributed (available in all
R-KIOSK / ). The sim costs €1 and comes with €1 credit.
Mobile internet will not work until you activate the card by making a phone call. I think this might be the problem woody1 had.
Internet costs €1/day, but because of the need for activation the initial credit is not enough - you need to make a phone call for which credit is deducted. Calling the free service menu didn't activate my card (although it should have, according to a person in an Elisa store). Also, checking the available credit with the USSD code is subject to a fee of a few eurocents (
the first time I see something like this on a prepaid sim). Top ups are available from €3, also from the R Kiosks in the form of a scratch card. Speed and coverage are very good. Validity is OK (1 year).