I wish to buy my wife's younger sister an iPhone
Wow, so you recently got married?
Yes, my wife is a good girl and she's so hot.
It might be a good idea to check with your wife before buying her sister an iphone, because that's quite a large gift. It's never a bad thing to ask before committing to that kind of purchase.
What... you don't want me to buy her an iPhone.
I'm not saying you shouldn't buy her an iphone, just to make sure that your wife is comfortable with it. She might think the gift is too expensive.