IPhone 4 has water damage, can it be fixed?

I want an iPhone and my friend is selling me one for $50 and I took a look at it and it's in really good condition (physically), he told me the screen was messed up and it's because he forgot his iPhone4 was in his pocket and it got water damage when he washed his clothes in the washer. The phone works perfectly fine, it just blinks a lot and the screen is faded and it just looks distorted. But you can understand what it says and all. I just wanna know if it can be fixed at some store (not apple, there are a lot of stores here that repair iphones) and how much would it cost? If it can be fixed I'll probably buy it and just get it fixed at the store and connect it.

What do I need to activate an iPhone 3GS bought from Craigslist?

I've never owned an iPhone. I have this guy that wants to trade me an iPhone 3GS, but I've never been on a contract plan, I usually get Virgin Mobile, but I broke my phone over the holidays. So what exactly should I ask to make sure I can activate this phone? And if everything is legit, and I buy the phone, what do I need to do to activate it? Virgin mobile also does a thing know where they sell iPhones, is there a chance I could just use this phone with their pay-as-you-go plans?

Added (1). If I need a sim card, how do I go about getting one? Do I just bring the phone to a cell-carrier, like Verizon?

Problems with my iPhone email?

When i send a email from my iPhone 5 to someone els let's say i send a email to bob@gmail.com and i hit send and it don't send to bob it send's back to me.someone help me.

Buying an iPhone online

Basically, I've found an advert online for an iPhone 5. The seller got it for Christmas from his dad, but already got a new phone, so is selling it. He has sent various pictures of it, and it is sealed and boxed. He has also sent a picture of the receipt so I know it's not stolen.

Anyway, he lives in Scotland and I live in London, so a local pickup isn't really possible at all. We're looking for a way for me to send the money, and him to send the phone in the confidence that neither of us will be ripped off by one of us not sending the phone/money.

Any thoughts?
P.s. I was going to send the money by bank transfer.