WiFi absolutely kills cell-phone batteries. I have tried it out on numerous phones, and in each case, it really drains the battery.
Why is that? Are you close to the tower, or does WiFi run at a higher duty cycle? Peak-power wise, GSM is the killer, but GSM can scale its power depending on transmission range...
The rest of this is pretty far off topic:
Ahhh... That's a load of........
I know that the airlines ban such things, but I think for two reasons. 1) Flight attendants have no idea what really is a risk (I wouldn't want someone sitting with an aircraft radio in 9D pretending to be ATC) and what's not. 2) they want people to pay attention during takeoff, landing and the safety briefing.
Here's a list of airlines which ban and allow GPS onboard...
http://gpsinformation.net/airgps/airgps.htm
And here's a publication from Boeing on it's investigation of every reported case of electronics interfering with a plane.
http://gpsinformation.net/airgps/interfere4.pdf
If you want to really have some fun, try and figure out how many people have their laptop's bluetooth and wireless enabled on every flight...
Well, I'm a little wary of using information from a GPS advocacy site as support for that argument. Garmin and Magellan say they don't know of any problems caused? Not surprising. That second PDF just says "well, we can't say anything for sure...".
I'm not sure if you understand just how sensitive these instruments are... GPS signals hit the antenna at 10^-16 Watts. There's about 70dB of difference in free space loss between a signal transmitted from the cabin and one sent from a tower 100mi away-- enough distance for a mW in the cabin to swamp a kW from the ground. There's a lot more that goes into it than these simple calculations, but that gives you an idea of the problem.
Aircraft instruments are designed to not be susceptible to most broadcast frequencies, and electronic devices are tested to not emit in protected bands. This means that the 2.4GHz from you Bluetooth is probably not going to interfere with an instrument designed to not be susceptible to it, but if you drop your BT card and a shield shifts, the arbitrary signals that leak out can do far more damage because they may be exactly in a band that the instruments intend to use. If you're using a GPS, you're likely to be generating frequencies in it that other GPS sets would be particularly sensitive to. GPS, TV and Radios have higher power narrow band signals as part of their architecture, which is why they get special treatment.
FCC testing only shows that the one factory fresh unit you submitted to the FCC met the guidelines.
Obviously it's unlikely that a problem will occur, but when you're responsible for suspending 400 people 6 miles in the air, you probably are going to err on the side of caution. My only point is that the airlines are much more likely to be making these decisions for the reasons they say they are than to make sure you learn how to buckle your seatbelt.
