In 2 days, the official corrency of Estonia will be Euro.
You are out of luck, if you don’t have our nice Kroons in your collections yet. But look at the bright side: after visiting Tallinn you don’t have to worry, what to do with any leftover exotic cash, as you can change euros easily to pounds back in the UK or just spend then next time you visit France…
Anyways, if you happen to possess Kroons already, you can exchange them indefinitely!