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I prefer my phone to be available as a phone. 5 hour battery life after using tethering just doesn't work out.
 
Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_1 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8B117 Safari/6531.22.7)

I use 3G all the time. I would definitely use the iPad less if I didn't have it so it's worth it to me. Plus I think I would rather have it and not need it than need it and not have it. I have use the mywi but it takes a toll on the battery.
 
If you have a JB iPhone get WiFi only.

If you don't have an iPhone or aren't JB, get the 3G.

Easy as that.
 
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