This impressive chart assembled by the web-based science "comic" XKCD shows how doses scale up in sieverts, the units by which absorption of radiation into living tissue is measured.

You can get an idea of the relative amounts of radiation various cellphone models emit by looking at their SAR, or specific absorption rate.

It was not until the 1950s that scientists had both good data on the absorption of infrared radiation, and digital computers that could speed through the multitudinous calculations.