When your pickup your new iPad today, you need to be sure you choose the right carrier if you’re purchasing a 4G model. That’s because AT&T and Verizon use different cellular bands for their 4G networks, so an AT&T iPad won’t connect to Verizon’s LTE network, and vice-versa.
They will share 3G connections, however. Buy a Verizon iPad and stick an AT&T micro SIM in it and you’ll have no problem connecting to AT&T’s 3G network.