remove data plan from iPhone?

Ok, i want to add a iphone 3GS to my parents family talk plan, but i do not want to pay for the data plan (no 3G, only EDGE here) so i devised a plan, i would:

Add the iPhone to their plan, pay for the 1st month of data (just maybe 2 months), then, put my sim card in my samsung sync (and keep it there), unlock iphone, put pay-as-you-go sim in iphone, then call AT&T and tell them the iphone broke (i dropped it into the sea) and since i am no longer using it, can i get the data plan removed?

I asked a online rep and they said yes (then again, their probably from india), Has anyone tried this before?

What it would cost:
Iphone 3GS..........$200.00
Activation...............$26.00
2 months data........$60.00

Total (forgetting 10 a month for phone):
$286.00

I have a pic of the rep saying yes

http://yfrog.com/67iphonep

So, will it work or will they make me keep data/cancel plan?

 

When you activate phone and switch SIM cards, its the same as not activating it. The card has to be activated, not the phone.