The best reason not to buy the new Verzion iPhone 4 is the increasing likelihood that the iPhone 5 will be released within the next 5 months.
According to ITProPortal, Engadget, and Gizmodo we can expect the iPhone 5 sometime between April and June of this year. Furthermore, we can also expect the iPad 2 to have support for both GSM (AT&T) and CDMA (Verizon) cell phone networks.
The iPad 2 will include a "super high resolution" screen akin to the iPhone 4's Retina Display and the physical screen size will remain the same. It will also feature both front and rear cameras, which will facilitate its use as a camera and video-conferencing station, via Apple's immensely popular Facetime app. You can also expect the iPad 2 to have at least one USB port, although some sources indicate it will have two. This implies that the upcoming version of iOS will contain a browseable file structure, just like an OS X or Windows PC.
One relatively new piece of information that has surfaced is that the iPad 2 will carry an SD card slot. I'm not sure how much I care about that, except that it does make sense for any device that will contain a camera.
Finally, it appears that the iPhone 5 will be "completely redesigned". One major upgrade will be a Cortex A9-based multi-core processor (the Apple A5). The current Apple A4 processor is a single-core Cortex A8 processor.
These are exciting times and lots of shiny things beckon to you from the mist-shrouded future. Make your purchases wisely kiddies. Patience is the key.