I posted about this some time ago, but I might have posted it on XDA. The site doesn't appear to be an official sprint site. Also, there is mixed answers, but it is generally said that it is for business customers.
To the best of my knowledge, that $100 credit was only ever for corporate accounts, not regular personal accounts, but at this point, I don't know if they even still do it for business accounts either.
This is correct....My sprint business rep confirmed that it is available if you are a business account and switching from another company you can get $100.00 credit per line.