No longer using the iPhone?

hello, I am going to have to switch off of the iPhone because of the data rates being too high. so, I was wondering, has this happened to anybody? what phone did you go to? and what is a good phone for me to go to? I really liked the iPhone simplistic design. conversation (string) text message viewing is a must. I would also really, really like it if I never had to delete the text messages! I am getting an iPad for everything else. so all my phone really has to be good at is texting. a full QWERTY keyboard is a must! any suggestions? the cheaper the better (since I am getting an iPad) thanks!