an idea

I am new to this forum so hello
I just bought a sidekick on ebay to replace my prepaid dead phonne and i called costumer service and they said i could use the sim card and just change the plan to the prepaid sidekick data plan but that costs a dollar a day i bought the fone for the internet but i will only use it on trips and such so i was wondering if i could call change my plan to sidekick wen i want internet pay the dollar a day for like 2-3 days than turn back. can i do that?????