For the OP, I suggest using an older iPhone. The first gens are dirt cheap on eBay or Craigslist.
For me, I have a cheap Samsung A107 that I got for free by redeeming my $25 AT&T giftcard that someone in this forum helped me get. I don't use it and it just sits there in my drawer.
There are some older phones I am looking at. If you want all the bells and whistles, then Samsung Galaxy S II. But if you want something just for texting and calling that also isn't an iPhone, I suggest something much cheaper and older (pre-2009) like a BlackBerry Bold 9000.
Right now, I am looking at a Palm Pixi Plus. I saw a CL ad being sold brand new for $50 last night. I text the guy and he told me it was already sold. This is one of the cheapest smartphones you can get and it was released last year. Has webOS in a candybar form. But finding the AT&T version at under $100 is harder to find than the CDMA ones. Just don't expect the hardware to be smooth even though webOS is a nice OS and the screen is small at 2.63 inches. But if you are lucky to find the GSM version of that smartphone for $50, it still beats getting used Motorola RAZR's for nearly the same price.