Hawt thats nothing... When I was 18 I signed up for cingular with zero credit and they charged me a 500$ dep and my mom wanted on my account so they charged me another 500$ dep. Cingular also ads things to your account without the account holders permission.
Example: We have friends overseas and we called them with our cell phones with phone cards. Everything was fine for 8 months or so then they added a feature called international calling so you wouldnt need a phonecard. We didnt like the rates they had so we just kept using the phone cards. Well the bill came and it was $1500... Whoa, Hmm cingular says that phonecards dont work anymore and the phones will use the default international plan.
Sprint is prolly a good place to be. 150$ aint that bad and plus you will get it back in a year. Its just a thing they do so they dont get screwed over.