Plans with bb and iphones and lenght of time to change options??

Ok heres my deal

i did a plan for 2 9700 bolds.. for free from a website and im on a family shared plan..

my wife didnt want here 9700 as she has a 8900 already for work.. she was seeking a iphone..

my parents also needed two new lines as there contract is up with tmobile...
so i was going to order 2 refurb iphones.. give one to my wife and keep one as a play phone for me in subsititute for my 9700 at times.

Now with the two new lines that the iphones are set up on.. i have two unlocked 8320 curves.. i wanted to use on those lines? Now i plan to pay for all services and not looking to get out of that. i just need to know will at&t care about this?

also i saw that i have to keep the iphone plans active for 4 months.. but at the time can i then switch to the bb plan for the two curves?

i just want to allow my parents to get there email eventually.. but i know i cant get mail on a bb with a iphone plan.. but i can vice versa.. which does me no good on these lines..

anyway att might let me make those lines a bb plan earlier? any info and guidence from some one who knows would be great.. not looking for i thinks or whatever im looking for real info that can help thanks