Question

Ismael

Answer 1

Let's call the Ameri-Mobile activation fee A, and the Cell-U-Later activation fee B.
Let's call the Ameri-Mobile monthly payment c, and the monthly Cell-U-Later monthly payment d
Let's call n the number of months

The cost of the Ameri-Mobile (in business, that's often called "total cost of ownership) is then:
(a + c * n)
The cost of the plan after n months is the activation fee, plus each monthly payment times the number of months paid
The cost of Cell-U-Later is, similarly:
(b + d * n)

You can even find out how many months you'd need to keep the plan for each plan to be equal (the longer you keep the plan, the better is the Cell-U-Later plan, because the activation fee distributes across a higher number of months), by plugging in numbers and solving this equation for n (but that's a bit more advanced):
a + c*n = b + d* n