AlltelU Plan Question

With the AlltelU Prepaid Pay-Per-Minute Plan, do you have to put more
credit into your account on a regular basis like most prepaid plans? For
example I know that with Cingular's Go Phone service if you put in $25
you get another 60 days of service. I've looked at Alltel's plan on the
web site and I couldn't find anything about how the service gets
extended. It looks like you only have to put in more money when you need it.