(...)talk about a tax of 3 CUC per day(...)
Actually it’s not a tax, it’s a regular service fee.
The information you are requesting can be found on the company website (in Spanish):
Etecsa – Mobile Phone Services- Contract and Activation
Additionally, there are wifi hotspots in most hotels and at a few public places in all major cities around the country, there is an access fee of 2 CUC per hour that should be paid in advance.
Credit:stackoverflow.com‘