I went to the Apple Store and got an Apple SIM, which cost $5. After putting it the iPad Pro and going to Settings>Carrier it gave me the option to choose from AT&T, T-Mobile, Sprint, and GigSky. Interesting that Verizon is not one of the Apple SIM partners, but I could always get a Verizon SIM if I wanted to go with them. So, it looks like everything is cool.
Thanks for the help!