ETECSA commercializes 3G Internet in cell phones since December 2018. In October 2019, they added 4G/LTE.
To activate the mobile data you need to know a few things:
Requirements to access the Internet for data in Cuba
You must have a cell phone that connects to 3G on the 900Hz band and to 4G on the 1800Hz band. (In phones sold by international companies, this detail needs to be reviewed, because companies often restrict the spectrum of bands on the phone).
You need to activate the APN Nauta. Users in Cuba who use Nauta mail already have it activated (see instructions for Android and for iOS). If you don't have Nauta mail, activate the APN and use the data network to access to free sites like etecsa.cu or mi.cubacel.net
How to activate Cubacel's Internet?
If you meet the two previous requirements, you are closer to being able to use Whatsapp in Cuba 😉
Just dial *133#
In the menu, choose the option Data.
There you will find the 5 options to activate the Internet.
Any of these allows you to use messaging apps and surf the network, but it is good to keep in mind that the purchase of data packages is much cheaper. In this regard, option 5 (LTE packages) is preferred by high consumers of data because it gives them the possibility of purchasing packages of 6.5 and 10 GB, though this it is only for cell phones that connects to 4G.
If you want to know more you can visit Fonoma Blog.