I understood the main reason for this legislation was to close the anonymous pre-paid phone accounts... that is they are not happy that you can use a phone without it being tied to your name/address. The whole thing is silly, however, as those with criminal intent will just use others credentials to purchase.
I don't think that's what it is. Anyone can get a Metro PCS phone without ID. I think it's the fact that stored value cards are used to launder drug money. The Treasury issued a Memorandum about this a few years back. They claimed it was the number one way people were avoiding taxes and laundering drug money.