i'm guessing no one read the buzz about wireless forum nor the announcement by sprint about this about a month ago:
http://community.sprint.com/baw/message/140691
This ONLY impacts customers who had poor credit. I think this has to do with those they deem high risk of not paying their account on time so they're trying to force ONLY those customers to do auto bill pay. While this may be a bit predatory, it's a business practice to make sure Sprint gets paid. If you had to have a deposit when you opened your account or if you missed enough payments to warrant this type of action, then it's those users only they're targeting.
FWIW, I've never even heard of anyone at any cellphone company asking for a deposit when I got a phone, that's probably because I have a very high credit score and good credit rating.