okay i think that might be the dumbs thing to do
Actually, it is sometimes the smart thing to do.
I have an inexpensive unlocked GSM phone sitting around. If I am going to be doing something outdoors and don't want to expose my iPhone to the risk of getting damaged, I just pop my SIM into the spare phone and off I go.
For those occasions when I want to run the battery all the way down and do a full recharge (which Apple recommends you do about once a month to keep the battery in good shape), I move the SIM card to my spare phone so I can still make and receive calls while my iPhone battery is dead.
If my iPhone should ever break or if I should ever need to send it in for service, I can move the SIM into my spare phone and have uninterrupted phone service.
If I am traveling overseas and don't want to risk incurring expensive data roaming charges, I can put my SIM into my spare phone and use my iPhone as a WiFi device and video iPod.
In other words, it isn't dumb at all.