How to completely reset a used iPhone without the password?

I'm helping a friend reset his new to him iPhone 4. He recently bought it from someone over the web. The previous owner stated he had already reset the iPhone but the iPhone still has his Apple ID. And to reset it completely I need the owners previous password. Can someone please help me?

Is it safe to jailbreak my iPhone 4S on iOS 7.0.4 using evasi0n 7?

I recently found out that there was a new jailbreak released for iOS 7 and up, and that it was being done through evasi0n 7. I've also heard lots of mixed reviews and news reports from the Evad3r team saying that the jailbreak is not 100% fully supported by saurik (Jay Freeman), for numerous reasons. Some reports are saying that saurik has not yet confirmed a stable version of Cydia for iOS 7, while I've seen many other reports that the iOS 7 jailbreak is now fully supported.

What am I supposed to believe? Is the evasi0n jailbreak for iOS 7.0.4 all good and safe to use? There was apparently a Chinese iOS hacking team involved with this new jailbreak, which added to the controversy of the quickness of this new jailbreak, so I'm a little unsure as to whether or not I should jailbreak my iPhone 4S on iOS 7.0.4. Any thoughts?

Added (1). The same goes for my iPad 2 on the same firmware - is that one all good?

How to hook my iphone up to a number?

I use my iphone as an ipod so when i take the bus to school it diesnt get internet, which is fine. But i was wondering if it was possible to hook my iphone up to a phone number. So that wat, i can use the iphone as an actual phone to call outside of home but still not have 4g or 3g turned on like i don't get internet ourside of home, like it doesn't charge for it at all

My HP computer keeps going limited?

My hp computer always goes into Limited connectivity. It doesn't do this on my ps3 or ipad or iPhone. Only our actual laptops. What can I do to fix this issue?

Iphone 5 Brightness Problem? - 1

So I damaged my iphone 5 using it in the rain a couple months ago. It shut off for 3 days, one of which I brought it to the apple store and they told me that it wasn't under warranty because the moisture strip things were activated which I figured. I put it in rice and after a few days it started working again fine, just with broken cameras.
So I've been dealing with my phone for the past 4 months because I can't afford a new one and recently it's been having brightness issues. The brightness has been really low and sometimes it goes back to normal for a little bit but it's really unpredictable. I was messing around with the brightness today and it just completely spazzed out and now I can only get the screen to flicker. I've tried turning it off and on and plugging it into the wall and the screen flickers and the touchscreen still works (I can shut it off using the touchscreen) and the vibrate works as well.
What I'm asking is, is there any way I can get the screen to work again? Is there something I can do if I plug it into the computer? Also, what kind of issue do you think this is? My dad thinks its a problem with the logic board so we've considered buying a new one and replacing it, would that be a good idea?

My Iphone 4s shows No Sim after being outside?

I went to play hockey at the outdoor rink with my iphone in my coat pocket and when i came back in to warm up i tried to use my phone and noticed it said "No SIM" where usually it says "ROGERS". I have never experienced this problem before and i want to know if its related to the cold weather and how I could fix this problem. I have tried powering on and off but with no luck.

I sent someone a message on mistake?

One of my friends asked for my other friends contact info and I accidentally sent it to this stranger who sent me a wrong number text. Is there a way I can get rid of that text? The texts were through iMessage. I have an iPhone 4. Please help because I don't want a stranger knowing my best friends contact info