How to add a service provider to an old iphone?

I have an old iPhone 4 my roommate gave me a few years ago. I've been using it as iPod and mini tablet around the house with Wi-Fi, but no cell service of any kind. It doesn't have a SIM card in it and I don't know what provider my friend had on it before. If I get one of these BYOP things http://www.bestbuy.com/...212&loc=1# will it work as a phone with calls and texts and still function as a iPod and mini tablet with my house's Wi-Fi?

I won't Have A iPhone For The summer?

My wh*re of a mother smashed my two iphones i need a job i'm only 15 and i can't find anything and she refuses to buy me another phone i'm really thinking about selling my body just for money

What iphone (or phone) to upgrade to next?

Ok so my phone contract runs out on Monday and I need to get a new plan As soon as possible. IIm verging along iphone 5s and 6 because I take a lot of pictures and I currently have a Sony Xperia SP which has horrid camera quality. I also use my phone a lot during the day so playing games and I've looked at a few reviews on the iphone 5s and a lot of people mention is gets hot quickly? That is the last thing I want! Also, anyone who has an iphone 5s could you tell me if you like the size? IIm used to bigger phones and I haven't held an iphone 5s in a while but it looks too small for me to be happy with and looks too fragile which is why I want the 6. Any recommendation?

Added (1). Also if anyone has any other phone suggestions similar to an iphone with good camera quality front and back would be great!

What is the name of a device that gives an iPhone more gb (storage)?

I have an iPhone 5c, and I only have 5gb. I've seen phone cases and stuff that give more gb to the phone. Is there a way I could use this device and have the pictures I take on my phone? Please don't say just get a new phone because I haven't had this phone for year and I don't want to buy a new one!

Added (1). I don't want to delete anything either

How to turn off the auto power off on an iPhone 6?

Okay, I didn't exactly know what it was called but it's the thing that when you don't touch your phone for a while, the screen dims, then turns off. I write my stories on my phone then I copy them onto my laptop. But my phone keeps turning off and it's annoying. So how do you turn that thing off in setting?