Can I use my iPad for AT&T or Verizon

If ou have an iPad 3, then yes, as I understand it, it is not carrier locked so you can use whomever you want.

If you purchased the new iPad (aka iPad 3) for use on AT&T, you can only use it on AT&T. There have been reports that iPads purchased as Verizon iPads will work with an AT&T 3G SIM card. However, you won't be able to use an AT&T 4G SIM as the companies uses different frequencies. If it's an iPad 2, it can only be used on the carrier it was purchased for.