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Perhaps you aren't persistent enough, but Apple's 14 day return policy is simply a piece of paper that means nothing.

I upgraded my 3gs after four months, I went from a 21" iMac to a 27" after three months and went from a black 16gb iPhone 4 to a white 32gb iPhone 4 after nine months!

If you are nice, handle yourself with class and communicate effectively with the right person in the store then I would say there is a 75% chance that Apple will take your product back and let you upgrade anywhere inside of 12 months.

That's been my experience.

What Apple store are you going to??? My Apple store won't budge on anything whatsoever..
 
You're paining yourself over nothing. Tethering is a piece of Piss and you always have your phone.

I have an iPad 32Gb 3g and I get prepaid sims 6 months at a time.

A few days after I activated a new 6 month sim I replaced my old phone with an HTC evo 4g and though I'd tether all the time but the battery on the evo struggles without tethering turned on so its actually easier to use the 3g on the iPad when I'm out and about for long days so I opted to go for the low end adjustable data plan on the evo (and only pay ~$22 a month for that data vs unlimited on the iPad sim)...
 
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