New customer up front charges

[#1]

Why does it state up front charges of one amount when you are looking to become a new customer .... but charge you a different amount once you go ahead with order?
And .. what is this monthly up front charge for exactly?

[#2]

Depending on what type of order the up front costs, which are detailed in the basket during the sign up journey, can range from the first months service (the second month is aligned 1 month after your service goes active) right through to a years upfront Line Rental Saver payment. There's also the possibility of new line install fees, postage for the router etc.
Hopefully my response above helps to explain.