I keep my cell phone in "airplane mode" almost all the time. I use VoIP on WiFi most of the time. When I do not have WiFI, I will use VoIP on 3G, but that's less than 1% of the time. Of course, this saves me a lot of money because I don't need a voice plan on my cell phone at all. (I do have the option to pay 25 cents/min and make voice calls, but I have never needed to do that so far. Instead, I pay about 1 cent/min for outgoing VoIP and zero for incoming.)

However, I do not do this just to save money. Here's a reason that is at least as important to me, if not more important: radiation exposure from WiFi is a fraction of the level from cellular radios.

Check this out:

http://www.acousticecology.org/docs/wifi.pdf

He says, in part:

 

This document is a summary of what I’ve learned during a few weeks of trying to decode

the conflicting information about the health effects of WiFi, or wireless computer networking

in the home. It was spurred by my frustration at the polarities of information, from techies

pooh-poohing all questions of health from WiFi or cell phones, to alarmist voices that

seemed unable to distinguish cell phones from WiFi, or to realistically address the current

state of the science investigating health effects (ie how much certainty there is at this point,

how many studies have been replicated, and similar standard steps in the maturation of a

new line of scientific inquiry). Nowhere, it seemed, was there a source of information that

looked at both poles and made an honest attempt to cross-check the assumptions being

made and to assess, with an open mind, the real situation. With the help of a few golden

needles in the haystack of chatter, here is such an attempt.

From the start, it will be helpful to bear in mind that the radio transmissions from cell

phones are six to twenty times more powerful than WiFi signals, and that increasing

distance from the WiFi base station decreases exposure levels dramatically. As the British

Health Protection Authority states, WiFi equipment creates only a fraction of the signal

people normally get from cell phones: "When we have conducted measurements in schools,

typical exposures from WiFi are around 20 millionths of the international guideline levels of

exposure to radiation. As a comparison, a child on a mobile phone receives up to 50 per

cent of guideline levels." The HPA has similarly equated 20 minutes of cell phone use with a

year of WiFi exposure. (Note: A convincing analysis of the HPA numbers suggests that the

difference is not quite so great, concluding that the WiFi exposure is actually one ten-thousandth of

the guidelines, and cell phone exposure closer to 1/200th, still a 50-fold difference, equating 20

minutes on a cell phone with 16 hours in a WiFi classroom—here assuming that at least one computer

is triggering the base station to be active at all times. In home settings, when the base station is

active only a small proportion of the time, the WiFi equivalent would be much more, more like 300

hours.) Still, these low levels may have biological effects. However, even the extremely

precautionary standards proposed by the BioInitiative project lead them to state that “this

target level does not preclude further rollout of WiFi technologies,” though they do

encourage wired alternatives, especially in schools where many computers are in use.