Can I buy a storm without having to switch to verizon's plan? I am on an alltel plan

I have two curves on my alltel plan which is $160 a month (with tethering) and my stepdaughter wants a Blackberry Storm. My mom has a storm on Verizon, and hates the touch screen so she wants to trade with me. Is that possible now that I am on verizon also, or will they be hateful and make me change my plan, which would then cost over $240 (with tethering)? They told me I could stay with alltel's rates when I changed over, and one customer service rep said I could use a storm, and another one said I could not. Ugh. Does anyone know?