My naighbor is using my wife for a iphone, how much MPS does it use?

How much data or MPS(mega bites per second) does an Iphone(4) use from ones wireless network?

My neighbor wants to barrow my Wi-Fi password… I want to know how much his phone will draw from my wireless network.
I have Time Wanner Cable and I pay 60$ a month for 15MPS…
How much could his phone use? I don't want my connection to be slow because he is using his phone for you-tube, email and other stuff… Any thoughts? I have 15 MBS but if his phone will take up to 5-10 MPS then that will really slow up my connection right?

You should never ever let a neighbor ever use your Wi-Fi. Ever! You will have nothing but trouble. Don't do it!