Well, I think a SIM is a SIM. It's the plan that regulates the data vs voice issue. I don't read Icelandic very well but it seems at least one shop at the Keflavik airport sells Siminn SIMS. They have a prepaid called "Frelsi" (Freedom) Within that there's a plan called "Sveigjanlegir" (Flexible) at three levels. Good @990 kr has up to 500 MB, Better @1990 kr has up to 1 GB and Best @ 3990 has up to 10 GB (1000 kr = $7.42)
The details are here:
https://www.siminn.is/thjonusta/simi...i-bodi/frelsi/