When i connect my iPhone to WiFi, why does it make my internet slow?

Question

Ok so the other day the weirdest thing happened to my internet, so i noticed that my internet speed was running ridiculously slow and like always i tried resetting the router which usually solves it, but it didnt. it turns out the problem was my moms iPhone, i know this because i tested this, i would run a speed test without her phone connected and i would get about 14down/1up and then i would run a speed test with it connected getting about .5down/.1up. My mom wasnt using any apps or anything that would use internet so something on my moms iphone was using the internet without us knowing and a lot of it. What could cause this to happen? Also as of the past couple days its starting to act normal again even with her phone connected. Our Wi-Fi is only hooked up to my iPhone, my sisters laptop and my moms iPhone. I even tried restoring the phone and although it didnt even have any apps installed or no browser open it would still use internet! And yes we have a password for the Wi-Fi. Please give me a good explantation for this, this has never happened to me before. I also noticed that when my moms phone wasnt connected the light on our modem would barely flash at all but as soon as i connected it the light would flash contstantly. As of the last few days it has been working fine but what would have caused this?

Answer 1

Setting up your phone "as new iphone" is covered in this article: http://support.apple.com/kb/HT4137
Before you connect to a new PC, make sure that autosync is disabled in Edit/Preferences/Devices, otherwise your phone will be wiped during the following sync.
If you have data on the phone you want to save, back up manually:
Disable autosync in iTunes, connect your phone to your new computer and right click on it in the device list and choose backup. iTunes will backup your phone without syncing. Transfer your purchases the same way, choosing "transfer purchases" this time.
When you connect your phone for the first time, all media content will be erased. But you can restore your settings and app data from your manual backup afterwards. Don't forget to set up at least one contact and event on your new computer to be able to merge calendars and contacts when you sync the phone for the first time.
Since changing your iTunes library will erase your phone again, do the same process when you change back to your normal PC.
About backups and what's saved:http://support.apple.com/kb/HT1766
How to back up and restore:http://support.apple.com/kb/HT1414
How to download apps for free again:http://support.apple.com/kb/HT2519