I don't know where you are at but here in Denmark I have unlimited/free SMS and using Netflixs test servers (Fast) I get 80mbit/s right now, inside my house out in the country.
Many I know have basically zero data in their plan as they don't need it for anything so there's no way WhatsApp or FB messenger can be cheaper than SMS. I think the price with only 1gb data and free SMS/MMS is something like $6.
I mean, by now several people have pretty much told you that things were and are different in other (and larger) parts of Europe than they seem to be in Denmark, likely having a big effect on the initial proliferation of WhatsApp and potentially other messengers.
Many I know have basically zero data in their plan as they don't need it for anything so there's no way WhatsApp or FB messenger can be cheaper than SMS. I think the price with only 1gb data and free SMS/MMS is something like $6.