I wuz scratchin' my head 'cus Amp'd has been contract-only durin' the soft launch, but 'parently they are not totally insane, prepay is on the way. From the RCRNews article:

Amp'd has said it plans to also offer prepaid rate plans shortly after launch.

http://www.rcrnews.com/news.cms?newsId=25114 »

Given dat their demographic is the 15-25 age group, that's good news.