this is how it works:
the 100 off the 1100 (or any phone) works cuz u sign a 2 year contract. this isnt for everyone, but im going away to college, and parents are taking over my cell payments cuz im quiting my job, (my anti "mommy daddy fund" explanation) so that way i forced my parents to get me a phone for next 2 years
its not a scam, some peeps even do it all for you on egay. there is a nice 35 buck a month plan for 1800 n/w and 200 anytime...which is what i got.
just fill it out and once approved they will send you the phone within the week and a bill within the month. \
edit: yes everything will go thru sprint, but on sprints website, they only offer it for select phones, coolcell and egay offer more phones. i suggest you do it asap as sprint also has an offer on the site for extra 500 min and you could call and try to argue to get it.