Pick up a refurbished Galaxy S II I777 from AT&T for $9.99, pay the sales tax on it of $45, pay for the upgrade to smart phone for $18, and buy a data plan.
if you can figure out how to do SMS messages on Google Voice for free, shine on ATT's text message plan.
Root it, and figure out how to use it as a hot spot for a laptop without ATT finding out or catching you. Might be OK to surf the web with a laptop or get emails, but don't use it to watch videos, certainly not anything over 360i, as that will give your data usage rate away to AT&T and they'll try to bone you. Maybe get your emails and phone to show up or forward to GMail or Google Voice , which does free SMS service also.
At&T's gig is to nickle and dime you to death for every little "plan" that they can. It's your job to beat them back at their own game with apps, rooting, widgets, kernels, software plans, etc. I say stick with 2.3.4 and don't ever update, it's not worth it, yet, it's a battery hog.