What a great sounding idea from Denmark. If you need a normal regular stamp in Denmark  just send a text message and receive back a code. You write the code where a stamp would normally go, presumably your mobile phone gets charged for the stamp equivalent, and no trip to buy a physical stamp is required.

How ingenious. Apparently letter up to 50g in weight cost the equivalent of 92p each. So the charge will be that plus the costs of texting. So compared to the UK not cheap but certainly clever.