You just don't. Their adoption of Whatsapp(at least in Spain), seems to have been driven by a period in time when WhatsApp was coming up that the plans sold by

You just don't. Their adoption of Whatsapp(at least in Spain), seems to have been driven by a period in time when WhatsApp was coming up that the plans sold by cell service providers were near unlimited data, but only X amount of calls/texts allowed to be sent per month. In the USA we had opposite plans during this time. Unlimited talk/text, but strict data caps.