ebay free wifi sim card

[catbell]

My husband will let me borrow his iphone when he is overseas but wants me to use a seperate sim card as he wants to keep his own sim and number.
He is PAYG but his free wifi has just expired, but as I would use it only for wifi i'm thinking of purchasing a free wifi sim card offered on ebay. He has an itunes account, so if I activate/ top up this new sim card for his iphone through his itunes, can I keep his account details or would the new sim mess up his settings. Thanks