My iphone 4 can't connect to Wi-Fi?

My iphone 4 will not connect to my home Wi-Fi. I type the correct pass word but it gives me the message "unable to join" or something like that.need help please

Can I switch my iphone 5 from Verizon to sprint?

Verizon is expensive and have a lot of hidden fees and I use up a lot of my data because I'm always on the Internet so my friends say switch to sprint because they have unlimited everything and they're cheap (we have a family plan of three which equals $190-$200 while my friends are $100-$150) but can I turn off my phone and have sprint turn it on or do I have to buy a new one? That's not a problem if I have to buy one though

Buying an iPhone 5c but keeping my plan?

I have a plan on T-Mobile that I'm very happy with. I recently decided to get an iPhone. After doing some research, I settled on the iPhone 5c. Apple sells an unlocked version for contract-free T-Mobile for $549 (this ships with a SIM card). My current phone uses a different type of SIM card, so I would need to have my number/plan transferred to the new one.

Could I just walk into any T-Mobile store (or even just call customer support) and have them change my plan over to the new phone? Or how does that work? I'm not buying my phone from T-Mobile, as the stores near me have a significantly higher price on the same contract-free phone.