Yeah, the Spartan setup process makes it seem like you have to buy their plans, but you most definitely DO NOT have to.
*IF* you don't want to mess with them being added to your cell plan, then yes, you have to do a Spartan plan... but if you have an unlimited cell plan, there is absolutely NO REASON to buy a spartan plan.
You will need to still purchase Spartan "Premium Credits" in order to access and use the app to view photos and manage cameras, but the premium credits are only $3/mo per camera.