Ugh, scalpers!
Couple of things to watch out here for are:
1) What if the iPhone isn't sold out... what if the supply is high enough that anyone who wants one can walk into an Apple store and get one. That would make it unlikely you can make much of a profit. Although, I guess if you sell it for around $600 or so, you'd still make a little bit of money.
2) You may have to pay for at least one full month of $30 a month data, or at least a few days worth of data. I am sure if you call customer service and tell them your brand new iPhone was JUST dropped into water or fell on the floor, maybe they will allow you to just pay a prorated amount or something. But then again, they may also say that they can only change it starting the following billing cycle. Who knows.
3) Keep in mind there is a $36 activation fee when you upgrade. That will not be refundable even if you make up a sob story to get out of paying for the data for more than a few days.
Why on earth would you extend her contract and leave her stuck on that crappy phone? What happens when that phone fails, breaks, or gets lost?
I see your point here, but if she is fine with a regular dumb phone, then if the current phone is broken or lost, the OP could just buy an unlocked GSM phone on eBay or NewEgg or something.
Last I checked, you can even get a RAZR (which works awesome btw, my wife used one until 3 months ago when we upgraded to iPhone 4) for around $49 unlocked.
I also went into one of them Tiger Direct stores in my area and saw that they sell some smart phones for $100-$200 without a contract as well. Not as good as a "Free" upgrade or a good smart phone, but then if OPs mom is not a technical person and just uses the phone for calls, texts, and occasionally snapping a picture there's plenty of options.
Its not like the olden days of 2004 and such when even the cheapest, crappiest contract-free phone was like $200+.